Chickens can get symptoms of Mareks at any time after exposure to a carrier. Wild birds or someone’s contaminated shoes can also bring it in. Hopefully, it is not Mareks, but some other issue. Do you have a rooster who might have hurt her while mating? Nerve damage from an injury, stuck egg, infection, or tumor could cause paralysis or lameness. Does she lay eggs? I would separate her so that the others do not harm her. A wire dog crate with food and water inside the coop can be good for that. What does she eat? Try getting her to eat some moistened chicken feed and egg. Poultry vitamins with riboflavin or B complex vitamins might be helpful in case of a deficiency. If you should lose her one day, your state vet could do a necropsy to give you a diagnosis. If that is not possible, a home necropsy where you open the abdomen, and examine the organs for anything unusual would be good to do. Take pictures of organs if you do one, and post here.
