Do you have roosters? Young roosters especially can be a little overzealous while mating. Could be she got injured that way.
Any open wounds? Check for bruising or swelling along the joints: bruises are green on a chicken.
Also check to see if her leg is dislocated: Stand her up, facing away from you. Then starting at her hocks, move your hands up her leg to where they attach to her body. You'll feel the joint-- do they feel the same or is there a bigger gap between the bones on one side?
If you don't see any wounds or bruising and dont think its dislocated, she's just got knocked around somehow and will heal on her own. But you've got to keep her from walking. Sucks, I know, but I had a hen with a similar problem. She was isolated in a smaller coop with a few buddies for two weeks-- no improvement, because she was still walking around, hopping up and down off the perches. 5 days isolated by herself in a large Rubbermaid container did the trick. (Poultry netting on a frame for the top.) She could turn around and also walk a few paces but that was it. She tolerated confinement well. If yours doesn't, maybe add some treats to keep her busy? Apple pieces (seeds removed), scrambled eggs, other treats