Sorry that your hen is not well.
From your description, I would suspect she's having reproductive issues. EYP is a possibility. It's not uncommon for a hen to have cancer, masses in the abdomen, etc.
Sadly, there is often not a lot that you can do but treat symptoms as they arise.
Crop problems accompany reproductive issues - inflammation/swelling, etc. can slow the process.
Antibiotics can sometimes be used as a supportive care measure to make a hen more comfortable but unfortunately they are not a cure for reproductive issues.
You can try treating her crop symptoms following the article linked below. An broad spectrum antibiotic like amoxicillin (Fish Mox) can be administered to help with infection, but do keep in mind that antibiotics can make an problem like sour crop worse.
I would work on keeping her hydrated. If she's able to be with her flock during treatment, that ime, is the best place for them to be, less stress for them and they aren't isolated.
https://www.backyardchickens.com/ar...w-to-know-which-one-youre-dealing-with.73607/