I would treat her for some more time with riboflavin containing foods, but getting the B complex would be wise. Make sure that you are feeding a balanced chicken feed, and then any added foods would not be necessary. A chicken chair or sling might be useful while you are treating. Mareks disease sometimes can cause curled under toes and leg weakness, more often on one side. Here is some reading about both riboflavin deficiency and Mareks:
https://thepoultrysite.com/publications/diseases-of-poultry/217/vitamin-b2-deficiency
https://www.merckvetmanual.com/poultry/neoplasms/marek’s-disease-in-poultry
Here is a good link with pictures of chicken slings and chairs:
https://www.backyardchickens.com/threads/versions-of-chick-chairs-please.1166308/
https://thepoultrysite.com/publications/diseases-of-poultry/217/vitamin-b2-deficiency
https://www.merckvetmanual.com/poultry/neoplasms/marek’s-disease-in-poultry
Here is a good link with pictures of chicken slings and chairs:
https://www.backyardchickens.com/threads/versions-of-chick-chairs-please.1166308/