She's 23 weeks old and plucking the feather out on her back. I've read that it could be lack of protein, but I'm using Ranch Pro 15% Egg Ration Crumbles isn't that is good enough? She's not molting. She's got plenty of room - I've only got 5 chickens and lots of space. There are no mites or anything on her skin. The other chickens are perfectly fine. What's up with her?