Yeah, the power's all about conservation of momentum - she doesn't lose any speed as she GOTTA GO FASTS, but she can't break into a 100mph slide unless she has some other way of moving that fast. And I thought about overheating, but I decided against it both for reasons already stated and because, well, friction is what causes things to overheat when they move too fast.

It's not that strong a power, but the weakness is mainly it's limited scope and its difficulty of use rather than an active weakness. It's tricky, but maybe I'm overthinking it.