Ride? Probably fine. Drive? Unless she's already 5'4 or so the ergonomics do not favor her. More than that, there's ample evidence that the neuroplasticity of anyone under 28 or so puts them at a disadvantage when dealing with the instantaneous decision-making processes involved in operating an operationally-complex device like a motorcycle. Not a crippling disadvantage, but they're more involved. Most young riders start out on dirt bikes, which have the advantages of (a) no traffic (b) substantially softer things to crash into (c) vehicular design intended for occasional spills. I mean, it might be a formative experience for her to eat shit at 11 on a Ninja 250 but I think you do have to contemplate how much you want your kid to eat shit on a Ninja 250.