the key doesn't have to be in the "start" position...
if you're jumping the starter the key would just need to be in the on position for the car to actually run, the motor will still turn over by jumping the starter even if the key is in the off position...
and there is a reason people hit starters...
if you're ever had a bad starter, or a flywheel with some fucked up teeth you would know that the starter can get stuck sometimes and will not engage when stuck, so if you hit it it will become unstuck and will then be able to start the car...
so it sounds like more than likely she knew exactly what she was doing...
except for the whole running herself over thing...
my guess is that she wasn't trying to hit the engine, but rather trying to jump the starter, which would explain why the key would be in the on position, and also why she wouldn't have yanked the hammer away when it started to turn over... but thats just a theory...
or it could have been in gear and she accidently jumped the starter causing the car to lunge and freaked out causing her to not remove the hammer...