In Thespiphobia, Gwyneth could never be considered as a super sweet girl. Mikayla is even worse. However - if you mess with the theatre's techies, or Mikayla's inventions, be prepared to burn more mightily than fuse in Hell. Not that Gwyn is oblivious to her techies' shortcomings - she's just the only one allowed to deal repercussions.
Charon McKay from Shadowgirls, especially when she pulls the so-called Slayer of the Elder Gods that was manipulating her daughter out of her mind, with just her bare hands and kicks it in the face. Also Christmas Snow when she stabs the guy who's responsible for turning her daughter into an Elder God Avatar through the heart. And this guy was making fricking scary sea monsters afraid of him!
Miranda Deegan of Dominic Deegan is one of the most powerful mages in the world most of the time. When her family or students are threatened, however, she is completely unstoppable. The necromancer Rilian once took advantage of this - he betrayed the Deegans' location to his age-old enemy, Helixa, knowing that Miranda would never let her lay a finger on them. He was right; Miranda killed Helixa (with her bare hands), and although it didn't take, she made a point of finishing her off the next time they met.
She took an infernomancer who tormented a friend of her son (the title character) and opened his mind to a world of arcane torture. And then she banished him to approximately the other side of the universe. This infernomancer had just attacked a classrom full of her students (she's the headmistress of the local Hogwarts) and killed three of them, though, so it's still valid.
An example of this and minor aversion of What Measure Is a Non-Human? occurs later when Vaarsuvius has to deal with the enraged mother of an adolescent black dragon that the party killed.
Vaarsuvius also counts, making a Deal with the Devil to have the power to save their own children from the dragon. They not only kill the dragon, but reanimate her head and use a high-level Necromancy spell to KILL HER WHOLE EXTENDED FAMILY — including eggs. According to V, that's nearly a quarter of all black dragons on the planet. This will ensure that no one in her family will come after V's mate and children again. Unfortunately, now V has pissed off Tiamat, the goddess of evil dragons. What's more, V inadvertently caused the death of many humans whose only crime was that they bore the child of a dragon (or hybrid thereof), or were related by blood to such a person, etc., etc. Vaarsuvius suffered a Villainous BSOD over that.
And, because we're not sure exactly what gender V or V's mate possesses, another Mama Bear moment goes to V's mate, who, after witnessing and perfectly understanding the above attack, still stands between V and their children holding only a stick. Inkyrius is specifically noted to be a noncombatant (a baker, to be precise) with only NPC class levels.
Darken, another D&D based webcomic, illustrates that even borderline cosmic horrors shouldn't bother the daughter of an ancient dragon.
Wigu has Romy Tinkle who, while a raging alcoholic in poor shape, was capable of getting the jump on and knocking out a ninja when her family was threatened by bounty hunters.
In El Goonish ShiveAbraham knowing that his opponent is half-human and half-immortal, saw only one implication, and mostly wrong one. The prospect of facing said immortal's reaction after he left her child within a hair's breadth of death somehow escaped his attention in all this haste. Immortals cannot interfere directly, but she's free to try killing him with mortals' hands...Isn't it surprising — where all those heavy boots flying toward his butt suddenly came from?
The actual animal variant appears in Sluggy Freelance. She will not, however, protect her cub from the local Killer Rabbit, and does as it says. Which happens to be letting said rabbit disguise itself as a cub, and then going around doing flagrantly criminal things, while people refuse to stop him for fear of angering what they thing is a protective mother bear.
But subverted when it turns out that bear was a male, the cub was his girlfriend's, and she was rather ticked when she found out.
Melika from Terinu raised the title character as her own son for eight years until he was torn from her by the Space Pirate that had originally found him as an infant. When she's finally reunited with him again after seven years, she's not only grateful to find him alive, she's more than willing to engage in prison breakouts and confrontation with armored Space Marines to keep from losing him again.
Melika: "Harm my cub and I'll paint this chamber with your entrails!"