I am so glad she is still hanging in there. Sounds like you might have been bitten by mites. They are very tiny and can be hard to see. I do not have experience treating chickens for mites, but there are many threads about it here. I put vinegar in my pigeons bath to control external parasites and use DE in the aviary. Just type "mites" in the search. I think you can pick up "poultry" dust at most feed stores. Unfortunately, they can be difficult to eradicate. You will need to do a complete clean out and disinfect of the coop and nest boxes. Old bedding and litter needs to be completely removed....hauled off or burned. A solution of Vinegar/Dawn/Water is safe to use. Make sure to saturate all the cracks and crevices really good. I'm sure there are other products available but I opt for what I always have on hand.
Sounds like you will be picking up a few supplies today. I would look for poultry vitamins as well. "Poultry Nutri-Drench" is what I use because they metabolize it very quickly.
Check with your Vet and see if they treat poultry. Some do and some don't. If they don't, ask for a referral. You never know when you may need a good bird vet! Just tell them what is going on with her and see if they are willing to at least check a fresh poop sample.
