It doesn't hurt to locate a source for a broad spectrum antibiotic and keep it on hand to treat a sick chicken rater than wait until you have a sick chicken. The wait for it to arrive in today's obstructed mail delivery system could mean a chicken dies before you can get it and start treatment. I order amoxycillin here. https://www.kvsupply.com/item/aqua-mox-250mg-capsules-100-count/P06184/
Is she still laying eggs? Her tail is down, so that makes me think that she has something going on with a reproductive disorder or a crop problem. I would continue to check her crop during the day to see if she is eating, and again in early morning when it should be empty. Poultry NutriDrench 2-3 ml orally may give her a boost. How do her eyes look to you? Are the pupils round and the color normal? In the one pic, the pupil is hard to distinguish as normal.
Thank you so much for this advice. I called around to places that would carry this and they said that antibiotics were pulled off the market thanks is to people taking it for covid. I will order some right away to have on hand. Do you add it to the water or administer directly and at what dosage? I have included a couple more photos of her just now. I have found eggs in the corner of the coop she always uses, but I haven’t actually caught her in the act to know for sure it’s her.