Check her crop first thing in the morning before she has access to food or water. It should be empty and flat. If not smell for a sour or rotten odor. An impacted or sour crop can be hard to treat. Here is a good article about crop problems:
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/