"This woman - you know, with the long golden braids and a bullet helmet, armed with a huge sword - has arrived to challenge them. She is Freada, shield-maiden daughter of Hrothgar! Now, um, *ahem*, the daughter of Hrothgar is supposed to be Freawaru, which means 'peace weaver' — not 'beater of ass.'"
Superman's Lois Lane gets more and more capable with each adaptation. She's not bulletproof or able to go toe-to-toe with most supervillains for long so she still needs Supes in the end, but where once, "Superman, heeeeeeeelp!" would have been immediate, now (in this case, at least since the 1970s in Superman Family)... well, if the Big Bad sends five Mooks after her, you don't wanna be Mook one, two, or three.
In one of the old Fleisher shorts, Lois was shown blasting away with a tommy gun at a gang of train-robbers.
Before they were canned, Siegel and Shuster were even considering having her figure out Clark was Superman, and making her Superman's civilian sidekick, similar to Margot Lane and the Shadow. They even wrote a script, which is floating around on the Internet.
Marian, the ladyfriend of the Lee brothers from the Double Dragon video games who gets sucker-punched and carried off in the original arcade game, became a policewoman in the comic and animated adaptation of the series and a female gang leader (who just happens to be the daughter of a policeman) in the movie. The Neo Geo fighting game version influenced by the film followed suit and made her into one of the playable fighters in the game who can stand on her own against the likes of Abobo, Burnov and even the Lee Brothers themselves.
I suspect that most modern viewers find it easier to identify with a Snow White who fights back. Spending years asleep in a glass coffin waiting to be awakend by "True Love's Kiss" is hopefully not something that girls today aspire to. We can fight for what we want, and we have a good chance of getting it.
Wonder Woman underwent this Post-Crisis; while she was already a superhero, the 80's version of the character played up her Amazon Warrior roots and even has her killing some of her foes.
The 2011 Post-Flashpoint reboot takes this up a notch by ratcheting up the Amazon warrior aspect even further.
A somewhat tame version of this trope occurred with Lois Lane's Post-Crisis reboot. Whereas her dominant characterization in the Silver Age had been typical shrieking helpless damsel and in the Bronze Age it was attempted to make her Take a Level in Badass, her revamped continuity gave her an army brat past and made her highly adept at hand-to-hand combat as well as a wide range of weapons and vehicles. The very first post-crisis miniseries in which she appeared had her beating up and commandeering the machine guns of a gang of terrorists holding her and a group of socialites hostage on a yacht, while Superman lets her take care of things as he obligatorily carries the yacht to safety. Needless to say, this pretty much makes him fall for her even harder than he had already.
In some alternate timelines, Mary Jane Watson has had spider abilities and used them as a superhero.
Random example for long-established characters: Shadow Lass from Legion of Super Heroes. Compare the fight with the Persuader. Some decades ago: Hides behind her shadows and cries for Mon-El to help. After-reboot: Blinds him and mops up the floor with him. (The generic setup is so similar that it well might have been an intentional lampshading.)
LOTS of characters are susceptible to this in fanfic.
Smallville's Chloe Sullivan is a prime example. On the actual show itself, for several seasons, she was a relatively competent scrapper in a fight, but certainly nowhere near expert-level in fighting skill. Not so in the wonderful world of Smallville fanfic, where Chloe (who usually acts as a Possession Sue in these fics) suddenly can trade blows with the best of them, even becoming a sparring partner for Batman in "Chruce" shipper fics. Some fics do make somewhat of an effort to make it seem more natural, by having Chloe start out with her canon level of skill and then undergo Training from Hell to gain her new level of fighting ability, but even these fics often have it happen way too fast, and the reader is treated to a montage of Chloe progressing from a merely competent, average-level fighter to a skilled, dan-grade martial artist in a matter of weeks. Now granted, on the show itself Chloe eventually didTake a Level in Badass and become a very skilled fighter...but by the time that happened it was already Season 9, waaay after most of these fanfics were written.
Hermione Granger from Harry Potter is another character who gets it frequently (as epitomized by this page's quote, "When the hell did Hermione become a ninja?").
Hinata in A Growing Affection. In the first book, she and Naruto become training partners, and Tsunade decides to put them as a pair through Training from Hell. By the middle of book 3, Kakashi acknowledges she is one of the ten strongest Leaf ninjas. She kills Madara towards the end of the last book. With a little help from Sakura.
The Little Mermaid II completely flipped the roles of Eric and Ariel. In the original film, Eric had to do all the action sequences and save a rather helpless Ariel in the climax. Meanwhile, in The Little Mermaid II, Ariel was so action-oriented when Morganna tried to kidnap her infant daughter Melody, that she actually ripped Eric's sword out of its scabbard while he stood there slackjawed. Eric was mostly useless in the action scenes. Apparently only one member of that couple can be an action team. Ariel was also generally far more adventurous and action-oriented on the television series, which took place before the first film.
Can we all stop to recognize that in the original Mermaid film, Ariel swam into a storm to a ship on fire and rescued a drowning Eric, which is quite an Action Girl thing to do? Also, in the climax, she full-on attacks Ursula, only ending up incapacitated because Ursula puts her on a dry patch of sea floor while she's still a mermaid. Ariel was an action girl all along.
Films — Live Action
Evelyn Carnahan in The Mummy Trilogy. In the first film, she is able to hold off most of her attackers (not so much a fully rejuvenated mummy, however), but not necessarily fight back. By the second film, after 10 years as the wife of a Ex-legionnaire, she's learned how to use Katanas and Sais, and aim guns with deadly accuracy.
Some of that comes less from her husband and more from her remembering her past life as an Egyptian princess.
In an attempt to make her an actual character (and cut down on the Loads and Loads of Characters), Arwen from The Lord of the Rings was given a big chase scene on horseback that Glorfindel did in the book. She was originally intended to fight at Helm's Deep as well, in order to allow her and Aragorn to actually interact, but it was cut in favor of sticking closer to the books. By that point, however, fans had already dubbed her Xenarwen. Liv Tyler even comments on this in the extended version's behind the scenes, saying she had done months of swordplay training to prepare for Helm's Deep, before the fans caught wind and dubbed her "Liv Tyler, Warrior Princess", and the idea was scrapped.
Hermione Granger didn't properly become an Action Girl until the fifth Harry Potter book and even then she was still inexperienced. In the films she gets Xenafied two stories earlier by riding around on the Whomping Willow (and somehow being able to use its momentum to throw Harry through the hole), being able to throw a pumpkin seed several feet through a kitchen window to break a sugar bowl, blast a cage door open and perfectly imitate a werewolf's call to save everyone. In the books the most she did was kick Sirius in the head to get him off Harry (oddly enough the film left that out). Also her Armour-Piercing Slap to Malfoy was changed to a punch.
Susan Pevensie in theChronicles of Narnia series of movies. In The Lion, the Witch, and the Wardrobe, she has a scene devoted to training, while she's never seen fighting in the book (despite being stated in "Prince Caspian" that she was already trained in bowmanship). In fact, when she is given her bow by Santa Claus in the book, she is expressly told not to use it, because "battles are ugly when women fight". Also, in the scene when the wolf attacks, she gives herself and Lucy time to escape by throwing a blanket at it. In the book, she just climbed up a tree and nearly fainted — though it's understandable, because would you be super coolheaded when a Savage Wolf who doubles as The Dragon is chasing you? Surely you wouldn't, kids.
Susan was also already trained as an Archer in the real world, whereas the much younger Lucy picked up her archery skills in Narnia itself. On the other hand, she was trained as archery as a sport than as survival means - which explains why she panicked horribly when Fenris was around, since until then she only had used her archery skills to point at blanks and not at living beings, much less wolves.
Keira Knightley plays a scantily clad sharp-shooting Guinevere in King Arthur. In the older pagan celtic versions of the tale Guenwifhar (Guinevere's original name) was a total badass.
In The Terminator, Sarah Connor is just an ordinary waitress who just happens to be the mother of the future savior of the world. By the time of Terminator 2: Judgment Day, she'd learned how to kick ass. Unusually for this trope, this is both explained and deconstructed, as her knowledge of the future apocalypse seems to have driven her over the edge and she has become almost like a human terminator as a result. This even gets some foreshadowing at the end of the first film, as, after the terminator is defeated, she drives down to Mexico to hook up with a gun runner. By The Sarah Connor Chronicles, she's up to Jack Bauer's Badass tier.
In-universe example in the live action Peter Pan film. Wendy's version of Cinderella swashbuckles with pirates trying to steal her glass slippers and gutting any pirate who dares to call her "girly".
Snow White & the Huntsman has Snow White donning knight's armor and leading a rebellion against the Evil Queen. In this version of the story, she hasn't just been forced to scrub floors, she's been locked in a tower for eight years. Also occurs in 2012's other Snow White adaptation, Mirror, Mirror, with the seven dwarves training Snow White to be a Combat PragmatistAction Girl.
Dracula's brides in Van Helsing. In addition to getting names and characterisation, they also get plenty of fight scenes and are a lot more competent than the supposed heroine. They're also given the handy little power of turning into harpy-like creatures whenever they feel like it.
Nancy Drew is another example like Lois Lane of this going in the opposite direction then swinging back with a vengeance. In the original stories of the 1930's, she was definitely more headstrong than a typical teenage girl of the time period, but her greatest strength was being stubborn and clever instead of being strong. After a near Orwellian Retcon of the stories in the 1950's, she became quite a bit more ladylike, with a lot more "smiling sweetly" and "asking nicely." However, after the Feminist Movement rolled around and the stories changed publishers in the 1970's, Nancy became a full fledged Action Girl. The Spin-Off series "The Nancy Drew Files" gave Nancy martial arts training and made the already-tomboyish George an accomplished athlete. The most recent series "Nancy Drew: Girl Detective" is a more partial example: They're not quite to the level they were in the "Files," but they have gotten a bit more clever, George is still athletic, but also a computer whiz, and the normally timid Bess is now a full-fledge Wrench Wench.
Live Action TV
In Happy Endings this happens mildly to Jane during Krav Maga and then much more dramatically to Penny after Jazz Kwon-Do. Jane is already kind of a violent, action ready person, but Penny is a very girly, Large Ham type of woman.
In Lost In Oz, Princess Ozma is mentioned as having been trained from birth to fight the Wicked Witch, and is apparently in her 20s. It's actually a subversion, as by the time the heroes rescue her she's lost all fighting capabilities and has been enchanted to be an eight-year-old.
Averted with Guinevere from Merlin. It would have been easy for the writers to simply give her a sword and have her display unlikely physical prowess in battle ...but she never does. Instead her worth is founded on her kindness and intelligence, and she's managed to get herself out of several dangerous situations by using her wits or stalling for time until she's either rescued by other parties, or manages to escape by herself. On the odd occasion when she does wield weapons in self-defense, she's portrayed as a competent but hardly skilled fighter. As such, she's something of a Base Breaker in fandom, with half believing she is a strong female character whose strength does not lie with the ability to swing a sword, and the other believing her a case of Real Women Never Wear Dresses.
As mentioned above, Maid Marian from the BBC's Robin Hood had a secret identity as the Night Watchman, a masked and hooded vigilante who was giving alms to the poor long before Robin came up with the idea. Despite Marian having a reputation as an Action Girl and Badass in the original ballads, the Night Watchman was clearly an attempt on the writers' behalf to have a "strong, modern take" on Marian, an idea that (in the context of the show) was somewhat unnecessary for several reasons: a) Marian already had a vitally important role as the spy and informant within Castle Nottingham, b) the concept was stuffed full of Fridge Logic (why didn't anyone notice that the NWM had breasts? Why did Marian need the guise in the first place considering taking food/money to the poor was hardly illegal? Where did she get her combat skills in the first place?note She claims her father had her trained so that she "would have choices", but given that Sir Edward spends the entire show fretting over her and forbidding her to do things means that this explanation makes even less sense), and c) despite being presented as a skilled fighter, the writers often had her thrown into the role of Distressed Damselanyway (and most of her best Badass moments were done without the disguise). For the most part, the writers get away with it considering their Marian was a three-dimensional character in her own right, and the idea fitted in well with Marian's rebellious attitude, but often the Night Watchman just felt like an excuse to have their lead female do an occasional back-flip or karate chop.
Once Upon a Time does this for a lot of female fairy tale characters. Snow White in particular is an extraordinary Action Girl more than willing to fight anyone who tries to keep her away from Prince Charming (at one point planning to snipe the Evil Queen with a magic bow and Instant Death Arrow). Little Red Riding Hood also kicks copious amounts of ass, though in her case, it's because she is the Wolf in this adaptation—the trademark red cloak is an enchanted item that keeps her from transforming, and once she finds out the truth, she uses her wolf form to help her friends—after making sure they get far away from her first.
Jacqueline was originally brought into WWE to feud with Sable and due to the latter's contract saying she couldn't take bumps, she came off looking rather weak. About a year passed and Jackie was able to show off her true ring skills, often getting in matches with men and even briefly winning the male Cruiserweight title.
The WWE Divas as a whole got a big boost in 2002-ish when David "Fit" Finlay came on board and was placed in charge of the division. More time and effort went into matches, storylines and pushing women who could actually wrestle. The Divas got to wrestle in rougher matches as well such as hardcore matches, tables matches and even a steel cage match. These days they tend to hover between this and how they used to be, though the recent hiring of Sara Del Rey in Finlay's former role has seen the division trending in this direction once again.
Trish Stratus is the wrestling queen of this trope. She came into WWE as a manager with an athletic build, but little actual fighting ability of her own, was shown as a submissive type for most of her early tenure, and then stepped up her in-ring work in a BIG way. She's now remembered as fondly for her impressive matches as for her impressive looks, and is one of only four women in the WWE Hall of Fame (alongside Sensational Sherri, Wendi Richter, and Sunny, who is the only one who WWE never used in a wrestling capacity, as she was a manager/interviewer/commentator).
The Dynasty Warriors series does this for Zhen Ji, Yue Ying, and Diao Chan. Sun Shang Xiang is a borderline example as she was known as something of an Action Girl by the standards of her time.
Fist of the North Star-branded spinoff Ken's Rage does a similar thing for Mamiya, taking her from The Load to a tricky and technical character capable of going one-on-one with the other powerful martial artists in the series.
Sonic the Hedgehog: Amy Rose was kidnapped in her first video game appearance in Sonic CD. She was given a Piko Piko Hammer in Sonic Adventure (well...Sonic Fighters) and was more than capable of taking care of herself. Prior to that, she had a mild form of this. Her Informed Ability of being a spunky tomboy who could fend for herself started coming into light with the racing games and Sonic The Fighters.. Though she's gotten less tomboyish over the years.
Yukiko in Persona 4 starts off believing herself to be incapable of taking care of herself. She is pretty, but shy and a bit helpless. When she gets her persona, her battle quotes reveal her newfound self-confidence.
Kairi in the first Kingdom Hearts game spent 80% of the story as a vegetable while Sora had to save her. In the second game she acquires a Keyblade and is able to kick plenty of ass to save Sora and the others. Dream Drop Distance's secret ending reveals Kairi is going to recieve formal keyblade training to be able to hold her own alongside her friends.
While Ariel in The Little Mermaid franchise qualified as an Action Girl, she was made into a guest party member in Kingdom Hearts and kicked more ass than she did in the movie or TV series (though neither of them had Heartless so who's to say she wasn't already like that?).
Way before Kingdom Hearts, the The Little Mermaid for the NES cemented her status as this. It's a surprisingly fun and challenging platform game not unlike the Mario franchise or Megaman
Yuna in Final Fantasy X-2. She goes from being a White Mage / Songstress / Summoner (All the stock 'female' jobs in that franchise) to being gun slinging Action Girl who thanks to the metagame Dressphere system, can be any of several 'boyish' jobs such as Warrior, Dark Knight and Berserker.
Princess Peach goes through this for every spinoff game. In the main series, she rarely does more than get kidnapped by a turtle, but in other games she tends to be a very strong and capable character. Most notably in Super Smash Bros., where she is a very powerful fighter for her weight class.
Super Mario 3D Land has Peach become strong enough to actually escape Bowser's Lair on her own. However, she is not competent enough to get away before recapture. Still, A for effort.
Paper Mario actually allowed the player, as Peach, to sneak around the captured castle and help Mario by gathering information, sending him useful items and badges, and essentially causing trouble for Bowser and his minions. She also gives Mario the power needed to finally beat Bowser in the final battle.
And in Super Paper Mario, Peach becomes a fully playable character who escapes Castle Bleck without outside help, argues with a nerdy chameleon (and breaks his date mod), and duels Mimi near the endgame. In short, this once frequently-kidnapped woman now kicks some serious ass.
Although she did need some help escaping the castle, because it was impossible to get out without help otherwise. Although she does take some levels, she is still comes under distress.
On a similar note, Princess Daisy. When she was first introduced in Super Mario Land, she was actually portrayed as a Distressed Damsel where she is kidnapped by the evil alien Tatanga, and Mario had to defeat the alien to save her. Now, she's a Tomboy Princess who appears in various spinoff games alongside Peach and prefers competing in sporting events more.
WWF No Mercy decided to make the female wrestlersnote this game predated the term 'Divas' playable competitively at the expense of realism and moveset accuracy. Trish Stratus, for example, used the koppu kick, rolling senton and choke w/bodyscissor in this game, even though at the time the game came out she was still in her "so bad she can botch a catfight" stage. They were also given enough stats to be competitively played rather than minimal stats like female wrestlers usually are in WWF/E games. Lita in particular was given a High Flying stat of 4, which made her not just competitive but fairly dangerous.
Rinoa of Final Fantasy VIII is pretty prone to getting kidnapped for about 75% of the game. Then she's suddenly placed into a coma and when she comes out of it she has sorceress powers giving her a Game BreakerLimit Break where her Magic stat is raised to 255 and she can cast spells without depleting her stock.
In The Legend of Zelda cartoon, Zelda got xenafied. She could use all of Link's weapons except his sword, and favored, of course, the bow and arrow. Her fighting ability seemed to swing wildly from episode to episode, from only nominally competent to almost as good as Link himself. In fact, there's several episodes where Link's Chronic Hero Syndrome and general stupidity gets him into trouble, and Zelda needs to rescue him.
In Scooby-Doo! and the Samurai Sword, 'Danger Prone' Daphne Blake is suddenly revealed to be a kick-ass martial artist good enough to be invited in a competition for the best in the world.