X2 for the mite and lice checking.
I see this all the time in Stars, to me it looks like just constant pecking and unless your not watching her 24/7 you don't actually know how brutal her friends are being.
You may want to separate her for a while and see if she grows some new plumage in...
Okay so I've posted these images before, but I didn't really get the information I needed. What do you think has caused this? My Red Star hen is pecked and bullied by the others but it doesn't seem severe enough to cause this. Recently she started growing new feathers over the bald patches...