Check her really well for lice/mites. The symptoms you describe sound like she's having some reproductive issues which can be common in laying hens. Peritonitis, cancer, salpingitis, etc. Crop problems usually go hand-in-hand with reproductive issues, so I would try to treat the symptoms and offer supportive care. She may perk up for a while hopefully.
Read this article for treatment of the crop. Usually if they have not been eating well, then treat for sour crop is the best course of action. Of course you can add in the coconut oil per the article, my hens seem to like it. Offer her some wet feed and easy to process treats like scrambled egg or yogurt.
https://www.backyardchickens.com/ar...w-to-know-which-one-youre-dealing-with.73607/
Read this article for treatment of the crop. Usually if they have not been eating well, then treat for sour crop is the best course of action. Of course you can add in the coconut oil per the article, my hens seem to like it. Offer her some wet feed and easy to process treats like scrambled egg or yogurt.
https://www.backyardchickens.com/ar...w-to-know-which-one-youre-dealing-with.73607/