In 101 Dalmatians, Perdita is perhaps the only female character in the old school Disney Animated Canon who truly enters combat and that's when her puppies are threatened. When it comes that, she's even better at it than Pongo.
Bolt: Penny's mother decks her agent (knocking him clean out of the ambulance) for daring to suggest ways they could exploit Penny's near death in a fire. (The fact that one of the supposed benefits was executive producer credit for himself was probably what set her off. Shaking Penny's stretcher (with Penny in it) and exclaiming "This is so great!" didn't help either.)
Queen Elinor in Brave is one of these both figuratively and literally, as she's cursed into the form of a bear. When her daughter's life is threatened, she throws off a dozen men pinning her to the ground and fights Mor'du, a cursed bear that seems to be immune to normal weapons, until she finally brings a stone column down on his head and kills him.
Mrs. Jumbo in Dumbo is branded a "mad elephant" and caged after she goes berserk trying to protect her son from some teasing kids.
Norma Jean from Happy Feet, despite her calm, loving demeanor, shows flashes of this. She is the first and only emperor penguin, in their extremely conformist and convervative society, to try to oppose the Elders, verbally lashing out at them when they force her son Mumble into exile. She also expresses great disdain for them during the graduation ceremony, as Mumble had not been permitted to graduate.
The Hunchback of Notre Dame has a tragic example with Quasimodo's Roma mother. Her baby was the only thing left in her life and she died trying to keep him away from Frollo. He caught her and another Romani on top of the stairs of Notre-Dame, tried to take baby!Quasi away from her, and in the struggle she fell down the stairs and died.
Esmeralda later becomes one with her son in the sequel.
The mother T. Rex in Ice Age when she finds her eggs are gone. She goes out and searches for them and was more than eager to eat Sid for taking them away from her.
Littlefoot's mother from The Land Before Time. For most of her screen time, she's shown to be gentle, caring, and nurturing to her son. But when he's about to be eaten by a "Sharptooth," she whips that fully grown, red-eyed T. Rex in the face with her tail, hard enough to knock him off his feet and send him flying into a rock. That one close-up of her face is the very definition of Mama Bear mode. Even after the T. Rex visibly tears out chunks of her back, she manages to strike him one more time (on a cliff in the middle of an earthquake, by the way) and send him falling into a chasm, and somehow turns herself around just in time to catch the two young dinosaurs with her teeth before they fall.
Please consider the fact that this is a Mama Bear 70 feet long weighing approximately 30 TONS.
Chomper's mom counts as well.
This is kind of a trend with LBT moms; Ducky and Spike's mom, for example, leaps into ice water to save her son from drowning in one installment and in another Petrie's mother flies through what can only be described as a typhoon to find her missing son.
Ursula from The Little Mermaid. Unlike the other Disney villains, she actually treats her Mooks Flotsam and Jetsam with love and respect, as if they were her sons; they in turn serve her loyally, and they probably are the most competent Disney villain's mooks ever. When they are accidentally killed by Ursula (thanks to Ariel pulling her hair when she was about to kill Eric, thus throwing off her aim), she first mourns ("Babies! My poor little poopsies!"), then goes into a psychotic rage, growing to a good hundred times her normal size and attempting to kill both Ariel and Eric with the powers of the sea.