Mareks can occur with symptoms of sudden paralysis early on, and very quickly, the symptoms can disappear, only to come back later. Tumors are common anywhere in the body. Wasting or starving can be a symptom. Many other things can look like Mareks, so getting a necropsy done by a state vet or...
Do you know if she was vaccinated for Mareks disease? That usually affects chickens when they are younger, but chickens can be exposed by a carrier later in life to cause symptoms. That could explain paralysis in one leg and weakness of her neck. Could she have been injured? Sometimes the crop...
Have you added any new birds to the flock recently? Sometimes it is hard to treat a sick chicken without ruling out a whole list of things. Has she had any history of eggs breaking inside, or laying shell-less eggs? Internal laying and egg yolk peritonitis is a common cause of illness in hens...