According to beautyofbirds.com/biting:
In many cases (particularly in cases of poorly socialized or abused birds), it is self-defense.
You should allow them to see your hand as friendly and not hostile, Because he/she probably was abused in his/her previous life.
As mentioned above - the trick is to teach them that hands are something good -- only to be ...
If the feather follicles are damaged in certain areas, then it's impossible for the feathers to grow back. Your bird will not have any luck in having all feathers again. I would recommend taking your bird to the vet to stop your bird from further plucking her feathers.
According to this article at backyardchickens.com:
If the feather follicles are damaged ...