This isn't Mareks. Mareks is a disease that can infect birds of all ages, but symptoms will typically only show in birds under or around 16 weeks of age. I have a flock diseased for life with Mareks, it is a horrible, horrible thing. Maybe she has a discomfort in her abdomen, such as internal laying or egg binding? Some forms of mycoplasmas can affect the ability to walk in chickens as well. Nutritional deficiency may also be playing a role. Its a shot in the dark, as there are so many possibilities. Do you have any pictures of her or her legs?
I just gave it in the drop form kind and then I gave them rooster booster and you can find that at local feed store or on amazon.
Rooster booster I totally recommend it you can just put 1/3 in I think it says and then you just do that for the course of 3-5 days and then after just put them on water. I give it to them 2 times a month and it is great.
Happy to hear your hen is doing alright. Keep us posted. She is getting to the age where chickens frequently begin developing issues. After about age 3 health problems are not uncommon. They can live well into their teens though! Birds typically recover well from impacted crops, I wish the best for you and your hen!