I wouldn't think it would be frostbitten, it gets a lot colder than that here and we have never yet had a case of frostbitten feet; combs and wattles, yes. She might have sprained it in a best case scenario, in which case she needs to rest it; put her in a pen or cage where she can't use it too much, and crush up a couple of baby aspirin per day to mix with her food. If it is a sprain it can take a long time to heal, we had a pullet with a leg or foot injury, we never did figure out what, who was in a pen for about six weeks before she recovered. She might also just have a glass splinter or something in her foot, which you wouldn't see. Feel her hips too; sometimes they can be injured or evem dislocated.
Another thing that comes to mind is a neurological problem So again you would want to keep her where she can't use the leg too much, and start her on high potency vitamins, preferably aviacharge. If nothing else you can use polyvisol, but I can't remember the dosage, should be on here somewhere if you search. Watch and see if she gets worse; if it's neurological they gradually decline over a period of weeks, and become more and more uncoordinated. Might be Marek's, but not necessarily, and even if it is, you would still treat it with vitamins.
So basically; a baby aspirin or two in her food; vitamins in her water. Good luck.
Oh also..give her the best food you can; whatever she likes; yogurt, cottage cheese, applesauce, are all good mixers to conceal the taste of meds in the food!
