cat gnawing off fur

Question
My girl cat started gnawing off her fur and has left two bald spots on her chest and belly, why has she done that?


EXTRA INFORMATION-
-she is three years old
-she took a bath two days ago(with the same shampoo as always)
-hit by a car half a year ago, so i dont think it is a nervousy thing
-was spayed when she was a kitten

Answer
I have no idea since I'm not a vet..
it could be something due to anxiety..or it could be due
to the start of a serious disease, say poor kidney function
I'd have her re-evaluated at the vet asap if it was my cat
Especially since she was hit by a car a little over a year ago  to rule out some sort of brain damage, any other serious illness..and even an acute illness that could be
relieved by having a doctor look her over
  I'm not a vet so I'm just telling you what I would do if it was my cat.
Thanks for the question