a speedster, but specifically with the power to manipulate the momentum of her own body.
this allows (limited and uncontrollable) flight and the ability to throw attacks at the speed of sound along with also just being able to move really fast.
however, the catch is that no matter how fast she might be able to accelerate herself and how strong she might hit, her body isn't really built to take that kind of punishment. she would spend a lot of time nursing wounds self-inflicted in normal combat.
also, the setting would be as physics-accurate as possible. this means that moving much faster than highway speeds would literally set her on fire.
she would die by accelerating her self to 90% the speed of light and creating a nuclear explosion
