Miki from the previous show is also an aspiring model, so she goes around changing her fashion occasionally, until she gets a 'perfect' look.
Erza from Fairy Tail is a Lady of War who loves to dress up, has over 100 outfits, and according to Word of God she once scared a major fashion designer into designing pretty armor for her.
Kuranosuke in Kuragehime, to the extent that he becomes a Wholesome Crossdresser so that he can pursue his passion without interference from his family of politicians.
Tomoyo from Cardcaptor Sakura would Once per Episode design Sakura some darn creative outfit. Sometimes the had some practical benefit but usually just to make her look cute.
Isis Egret of Magical Record Lyrical Nanoha Force, who has dreams of starting her own fashion label despite coming from a family that specializes in guarding important people.
Mary Jane Watson in the Spider-Man comics, who at one point was a fashion model. She is kind of a Tomboy in personality, though, in that she's very direct and enjoys sports.
Films — Animation
101 Dalmatians: Cruella de Vil's obsession with fashion, especially of the furred variety, is her entire motivation, leading her to acquire nearly a hundred puppies to make into clothing for herself. Since she is the evil variety of fashionista, she lacks the typical good looks, having instead and exaggeratedly thin body with protruding cheekbones and a great deal of make-up.
Films — Live-Action
Most of the women (except Andy) in The Devil Wears Prada. Nigel, too. Of course they do work for a fashion magazine and Andy does start "drinking the kool-aid."
In A Knight's Tale Jocelyn likes wearing different clothes and dressing to match her knight because a flower is only as good as its petals.
Rachel in Animorphs is one of those people who always know the right clothes to wear and how to look like they just walked out of one of those fashion magazines girls like. Shopping for clothes in the mall is her favorite hobby.
Alice in the Twilight saga. Loves dressing people up and throwing parties, especially if Bella's involved. She not only organized Bella's wedding, but packed her honeymoon suitcase, dressed her up in a cocktail dress and stilettos for her first post-vamp hunt, and filled up her closet at home mostly with high-end, fashionable clothing while Bella would rather wear jeans.
In Lonely Werewolf Girl this is the Hat of the Fire Demons. Standout character is of course Malveria, but Werewolf-fashion designer Thrix runs a close second. Showing up in the wrong dress could start a war you know.
Anyone who grew up reading The Baby-Sitters Club series will remember the obligatory description of Claudia's outfits as the highlight of the otherwise virtually copy-and-pasted introductory passage in each book. She was also the artsy one, and her dress sense obeyed no laws of fashion except her own, but we're assured that "on her, it totally worked" every time. Her best friend Stacey was from New York, which was treated like it was proof of fashion consciousness in itself.
Time Scout: Margo dresses well. Timeless class. And when she first encounters Connie Logan's shop, she practically orgasms.
The French, in British statesman Lord Chesterfield's Letters to His Son. "Fashion is more tyrannical at Paris than in any other place in the world; it governs even more absolutely than their king, which is saying a great deal."
Jessamine Lovelace from The Infernal Devices is very concerned about how she looks, and it's she who takes Tessa out to buy new dresses.
Raven Baxter of That's So Raven is a slightly unusual example, since Raven herself lacks supermodel proportions. Fashion design is her passion, however, and she makes most of her own clothing. The plots of several episodes revolve around her interest in fashion and making it a career.
C.J. on The West Wing, a bit, though it's also brought up as one of the ways she has trouble being taken seriously as a female White House press secretary (people either focus on how she looks rather than what she's saying, or assume she does that).
When earlier female American Idol judges started commenting on how a contestant looked, it was usually a sign that they couldn't find anything good to say about their performance. Nicki Minaj, on the other hand, is almost always giving commentary/suggestions on their style choices and still commenting on the performances themselves.
Friends: Rachel, who works her way up the fashion career ladder and is the Girly Girl to the more practical and intelligent Monica's Tom Boy.
Fiona Coyne from Degrassi is a talented artist and is also very interested in fashion, as shown through her unique sense of style.
Rachida Dati, former Justice Minister, is portrayed as quite fashion- and shopping-obsessed (at the expense of any political savvy).
Karl Lagerfield, on the other hand, is the serious fashion designer and critic version of the trope.
Monster High has Clawdeen Wolf. Unlike most fashionistas though, she is serious about going into the fashion industry in a business-minded way and in her 2011 doll with diary the first entry mentions her AP class in fashion.
Animal Crossing has roving fashion consultant Gracie, a giraffe. Gracie will judge your clothing in some of the games, and in all games she provides the player with her signature clothing line. She is depicted as having overall very expansive tastes.
One of the oldest examples is Yuko Asahina, in Tokimeki Memorial. This makes her one of the most special girls in the cast, as the secret to win her is to go to dates to the trendiest places or shows of the moment For MassiveRelationship Values.
One of Emilia's background traits in Yggdra Union; literally almost every item she ever uses is an Elegant Gothic Lolita-inspired accessory or jewelry that she's personally made.
Shiki from The World Ends with You has a talent for sewing and mentions bringing to life the designs of her friend Eri. She serves as a contrast to protagonist Neku who professes no knowledge of trends or fashion and barely notices damage to his own clothing. Although by damage, Shiki means "one of your buttons is slightly coming off."
Duncan from D4 is a particularly crazy example. His hair is a green swirly cone, and he brings a mannequin named "Sukey" everywhere he goes, and dresses her up just like him.
Junko Enoshima from Dangan Ronpa is a very famous kogal model known for her extravagant tastes and she has this as her Super High-School Level title. Except that she's not really Junko herself but her twin sister Mukuro Ikusaba disguising as her, as they made a Twin Switch before the start of the series. And the real Junko? She's the Big Bad and the mastermind behind the entire events of the series, which includes killing Mukuro and then using her corpse to fake a murder.
The titular character in Nicole is very interested in fashion. She has a number of different outfits that she wears throughout the game, and she expresses genuine distress at the ugly uniform she's expected to wear at work. She actually rolls up the sleeves and legs to turn it into a romper.
Kanaya in Homestuck has this as one of her defining character traits. It stands out especially because her species isn't interested in fashion whatsoever. She is the only troll to start out with multiple different outfits (that she made herself) and whenever anyone wants some sewing done she is the go-to-troll for that.
Self-proclaimed by Rhonda in Hey Arnold! and brought up in almost every episode she's in... despite her limited wardrobe. She does have the tall, straight body-type though.
Rarity, from My Little Pony: Friendship Is Magic, is an example of what happens when the management insist that a cartoon aimed at preteen young girls has to have one of these, but the showrunner is bound and determined to have the series pass the Bechdel Test. She dodges the stereotype by being a producer rather than a consumer: instead of being an obsessive shopper, she's a fashion designer who owns and runs her own boutique. As a result, most of her episodes focus heavily on her efforts to succeed as a fashionista and often deal with the business end of the job.
Stella from Winx Club is this, or strives to be this. She makes ready use of the large amount of money she has (being a princess and all) and shops a great deal. She gives her friends tips or comments on their style frequently.
Cornelia Hale from W.I.T.C.H. tends to be this. She loves shopping for clothes . . . and shoes.
Marie Antoinette was supposedly a huge fan of fashion in her day, making her dressmaker, Rose Bertin, a celebrity of sorts.
WWE's Natalya. She was initially portrayed as a tomboy but that got dropped since she's not like that in real life at all. Just look at her shoe collection.
Peyton R. List, who plays the aforementioned Emma in Jessie, is this in real life. It was mentioned in an interview that Emma's original wardrobe prior to her being hired was cute but somewhat normal compared to Peyton herself. As a result the wardrobe people used Peyton's own style to help make Emma more of a true fashionista. They sometimes collaborate Peyton's clothes with the wardrobe choices for Emma to create even more outfits.