I used to breed rabbits, and they get this same disease, although it MAY be from a different parasite. I didn't study it much beyond remedies in rabbits to know if chickens get the same one. But here is an option. It may be a LONG shot, but it worked for rabbits...
The parasite we had trouble with, affected the brain of rabbits. It would get into their heads and mess up their equilibrium. Even when treated successfully, the rabbit still held his head slightly tilted, although no where NEAR as bad as having the actual disease.
The trick was a very timely shot of Ivermectin. This is sold at
Tractor Supply stores WITHOUT a prescription. The brand name is usually Ivomec, and it is often refrigerated in a locked cooler. But again, you do NOT need a prescription to purchase it. You will, however, need a syringe to administer it. The smallest gauge they offer is usually 22 or 25. Go with the higher number of the two, since it will be smaller.
(NOTE: I actually used my mother's insulin needles for this. The gauge is incredibly small - 29 - and the syringe itself is small enough to deal with the tiny amount they will need.)
And it IS possible to give a chicken an injection. I did that once with tetracycline for an eye infection one of my hens got. Just find some skin way down under those feathers, pull a "pinch" of it away from the underlying muscle and fat, and inject the medication in the little triangular gap right below the part you have pinched.
For a medication like this, you will need 1/10th of a cc, or 1/10th of a ML. If you're using a diabetic syringe, it would be consider "10 UNITS". If it is in advanced stages, you can safely give them twice as much, BUT NO MORE.
If that works, let me know. But at this point, it probably can't hurt anymore.
she seems as though she has given up this fight. Considering the length of time and the lack of improvement, I decided to NOT force feed this time 
I've made her comfortable and ill let her go
