you might want to read all of the responses that I got to a thread I started two weeks ago. The symptoms you mention are similar, although not quite the same, as to symptoms we have in a young bird. You can find the thread by searching by my login, zylechicks.
We have determined that our bird has Mareks disease. It is deadly and highly contagious so worth adding to your list. Please check it out. If your hen has Mareks you need to know about how to quarantine her and clean your coop. The posts on this thread are very helpful if disturbing. One thing to point out, our bird had been getting progressively better. She was eating more, drinking more and had regained her ability to walk. From what i can tell, none of that matters now.
I hope your bird doesn't have this disease but if she does, then you need to learn as I have about the consequences so that you can protect any other hens who were exposed to her.
Good luck.