What B vitamins have you given? Riboflavin (B2) is important in chicken leg health. I recommend using human B complex (or Super B Complex) vitamins which has all of the B vitamins including riboflavin. You might try making her a chicken sling chair for periods throughout the day, and then...
Does she walk with a wide stance when she does walk? Does she seem to favor one leg? Do you have a rooster who might have hurt her? Does she still legs eggs regularly? Can you try some human B complex 1/2 tablet orally crushed into her food or given orally every day for a few weeks? If you can...