What you are dealing with is some form of neurotoxin poisoning or possibly Marek's, which also affects motor function. And no, chickens don't always die from Marek's, most do, but a few can get better, though they always will have the disease. And chickens can get it even if vaccinated. It's like our flu in that there are many strains and the vaccine doesn't allow for developing resistance to some of them.
If it's Marek's there really isn't anything you can do. If it's a toxin, you might be able to counter it with and Epsom salt drench about a teaspoon in a cup of water. You may have to syringe it into her beak. This purges the intestines to help prevent further absorption of the toxin. You can follow up with a molasses flush which does the same thing but it helps condition the intestines.
After that is vitamin therapy. Vitamin E oil 400iu with a sliver of selenium and B-complex daily to help repair the damage to her nervous system.
This may not work if it's Marek's or if she's already suffered irreversible damage to her nervous system. But it's worth a try.