Well, physical injury should always be the first consideration. I always hard to even mention Mareks as a possibility, but it can be a possibility. Usually if a riboflavin deficiency, which normally affects both legs, is treated soon with extra b vitamins, one should see signs of improvement within a few days or a week. Leg bone deformities that some chickens are born with and injuries can sometimes cause a ruptured hock tendon. Since we are not vets we can just make suggestions. If you later would like to test for possble Mareks, some poultry labs will test blood or feather shafts for Mareks. Also if you should lose her, your state poultry vet can look for Mareks. You may want to limit her activity to keep her from jumping up and down since an injury might not have time to heal.