Feather picking is often from boredom or being too crowded, or from a protein deficiency. Other times it can happen on the roosts if birds are above each other.I wondered about that, too. It could very well be. Anything I can do to stop it? I have seen this chicken pick at herself, too, but she may be doing that from the irritation.
What is the protein content of your feed? I'd suggest 18-22% protein. You can dust her just to be sure. It wouldn't hurt.