If you like to give pain medication:
Can’t help you with a diagnose. Hope she gets better.Aspirin is absolutely fine for chickens, I have used it on the advice of my avian vet as well.
You want to treat at a rate of 25 mg. per lb of body weight. Or approx. 1 baby aspirin per 3 lb's. I crush them between two spoons, add a couple cc's of buttermilk and suck it all up into a needless syringe and dose the bird that way. The buttermilk also helps buffer the aspirin. We were doing that dose on a four pound hen twice a day.