One of my girls is pecking the feathers off of the others neck. I have not seen her do it, but I cannot figure out what else it could be. When the large white one was brooding the others feathers started coming back. I have checked for mites and even treated her with DE but that has not helped. I need suggestions. She does not seem bothered by it, and continues to lay eggs regularly, but this has been going on for at least 6 months and she looks so bad.