I have a pullet with Marek's who suddenly wobbled at 4 months & couldn't walk in a few days. She's still alive & has gained weight, after 4 months more, but the nerve damage to her was permanent, I think.
There are other symptoms which usually go with Marek's. One is "depression" or seemingly listless & drowsy. Another would be disinterest in things in general, including food. Marek's often attacks the eye(s/) in chickens, making at least one eye blind & looking like there is glaucoma. My hen didn't have this. Vitamin E, A, B-Complex, or something like "Poultry Drench" would be great for her regardless. Flax seed/oil as well, for EFA's .
It's great that she has a good appetite. This is what makes it sound less like Marek's.
To relieve symptoms of pain & numbness in her legs & feet, you can use homeopathic Hypericum 6C. It took my pullet from not walking at all to almost running (wobbily) in 5 days. It should slow down the progression of nerve damage.
It's available at Whole Foods or another health food store, or via internet.
As to how long it takes for it to run its course, I've read other people on BYC who said 4months or 6 months. I've also read it could take a couple years total before it recedes.
Keeping her well-nourished and out of stressful conditions (like heat) is one of the best ways to help her immune system fight it off. As long as her appetite is good, and she's eating on her own,she should fight the virus.
Keep checking her eyes to make sure she can see well to eat, and check out all the other information on the Net and here regarding Marek's. Good luck!