I would bring her inside to keep warm, get her to eat and drink well for a few days to build her strength, and then try to put her back out in the coop with a heat lamp for a few days. Feed her some vitamins with electrolytes in her water, some probiotics or a little plain yogurt in her feed, and add some egg, tuna, or liver to her normal feed. Adding water to the feed to make it soupy may make her eat more of it. Using a high sided bowl containing her food along with wetting the food may make it easier for her to eat all the time. She also might benefit from having her beak trimmed. The Chicken Chick.com has a good article on scissors beak chickens and beak trimming.