Well, unfortunately at her age and with her symptoms this sounds like Mareks, but a head injury could also do this. If she dies, or you decide to cull her, it would be good to get testing to see if it is Mareks, so that you can go forward. Your state vet lab usually can do a necropsy and testing for Mareks if indicated. Here is a list of state vets to contact:
https://www.metzerfarms.com/poultry-labs.html
https://www.metzerfarms.com/poultry-labs.html