Very good suggestions from Wyorp Rock and Chick Nanny13. Can you post a picture of her comb and her grey eye? A hidden wound could become infested with maggots, so good to look her over again. I have heard of chickens becoming lame due to an internal infection in the spleen or elsewhere, putting pressure on nerves causing paralysis. We always think of Mareks with lameness, but there can be other causes. If her eye is turning grey, though, that points more to Mareks.