She could be developing sour crop. Here is a good article that you may want to read to help know if she has it, and try to treat her:
https://www.backyardchickens.com/ar...w-to-know-which-one-youre-dealing-with.73607/
https://www.backyardchickens.com/ar...w-to-know-which-one-youre-dealing-with.73607/