Yes, you can have an odd ball hen, but make sure she is safe within her small flock. While you may not see acts of aggression, remember you are not there 24 hours a day, and your young pullet may be the subject of teenage bullying.
Hopefully things have resolved. It does sound as if she is being stressed. Possibly by her flockmates, and most definitely by the visits of the hawk. Hopefully things have improved. Welcome to BYC.