My chicken has been like this for months. I have tried everything, Washed, bought anti-fungal and yeast infection spray, dust bath, vitamins. She seems to be in a lot of pain. Very vocal. The feathers she has are mostly just spines. I know its not lice or mites. I thought it may be vent gleet so I treated for that, or water belly also seems like an option but even though her chest is red she doesn't seem to that the swelling.