Teenage mutant ninja turtles(2012).
See this in my Story Dump fanfiction
This takes place before the turtles and Splinter mutate.
A young teenage girl called Jenny is walking her dog one day when she comes across a canister of ooze, curious as to what it is she takes it home with the intent of giving it to the police later. While at home she accidentally spills some on herself, it causes her to pass out and when she wakes up she finds herself mutated.
Jenny's new mutant form is almost twice her original size, she has a long lizard-like tail and wings, clawed hands and feet, fangs, her once-brown hair is black, her once-green eyes are red, and her skin is blue and tougher than human skin; she basically looks like a blue dragon-woman. She also has increased strength, senses and reflexes, and she can glide with her wings but not fly.
Fearful for how people would react Jenny runs away with her dog. Over a few weeks Jenny finds her way to New-York and takes up residence in an abandoned train station (yes, the one that's turned into the turtle's lair).
While out looking for supplies Jenny spots Splinter's confrontation with the Krang and watches as he and the turtles are hit with ooze and mutated. Jenny scares of the Krang and takes Splinter and the turtles to her home, she explains to Splinter about how she was mutated as well and offers to let him and the turtles stay with her. Splinter agrees seen as he has little other options.
Over the years Jenny becomes the mother figure in the turtles' lives, though she remains just a friend with Splinter. The turtles eventually nickname her Mama Dragon because of how much she looks like a dragon and her protective nature over them. Jenny manages to convince Splinter to allow her to take the boys trick-or-treating on Halloween nights after they turn five, since people believe they're just wearing really good costumes.
Like the boys Jenny learns how to fight from Splinter, her main weapon is a kusarigama.
The family find another affect of Jenny's mutation as the years go on, her aging rate has become much slower than normal, so she looks likes she's still waiting to enter her twenties when her sons are teenagers and they go above ground on their own for the first time.
Jenny is hanging out with her sons when they're attacked by the foot, along with Dogpound and Fishface, the turtles decide it'd be in their best interests to sit the fight out and let their mother take them out instead, which she does because she's angry at them for hurting her sons.