Have you examined the bottoms of her feet for injuries? Are the feet swollen at all? How about discoloration on the scales? Chicken bruises can be green or gray.
It may not be an injury. It could be a tumor on a joint. Arthritis in chickens can be caused by a virus. Petroleum distillates can cause neural toxic poisoning, resulting in brain damage, not enough to kill a chicken, but enough to make them go lame.
Lameness in chickens is about as difficult to try to diagnose as general "my chicken is acting sick" symptoms.
If you don't detect an obvious break, I suggest letting her rest and keeping her off the leg for a few days, and hopefully it's something simple that a little rest will cure. You can give her one baby aspirin two times a day for pain.