I had a chicken badly bitten by a dog about six weeks ago and she has almost fully recovered, based on that experience this is what I recommend. Check that she has no open wounds anywhere on her body. If she does then these need attending to immediately. (Open wounds: swap with antiseptic and water solution - I use dettol in warm water - dry off with clean towel, sprinkle liberally with turmeric powder and leave uncovered. This will keep the flies away and allow the wound to heal naturally. She will look oddly coloured but don't worry about that. Ground Turmeric powder from the spice section of your supermarket will do fine.) If she has eaten and had something to drink then put her into a cardboard box, close the flaps and put a towel over it. She will be in shock and she needs rest and quiet. Tomorrow, you need to place her in a separate area, so the others can't attack her because she is 'down' or use stand-over tactics and take all her food. I kept mine with the flock during the day but brought her inside at night and put her in a cardboard box with a towel over it at night. You need to keep her warm and well-fed. If the leg is broken get it splinted by a vet. Don't give her any strong meds that may upset her delicate digestion system; natural remedies are best for chickens. Give her chopped up greens, chopped tomatoe, chopped cucumber (especially good), meat or fish, wheat and put a vitamin supplement in her water for good measure. Keep the food up and the stress down. I constructed a temporary 'run' or cage in the middle of the flock by placing a large strong wooden box (for shelter in wet weather) on the ground and running a temporary roll of tall wire mesh around some four foot high metal stakes that I had driven into the ground. The flock continued to eat and socialise around her, she wasn't lonely but was out of harms way. On a wet day I kept her under cover, one day it was so bad that I kept her indoors most of the day and fed her in a cat cage and because it was only a twenty four hour period of really bad rain it did her no harm. Your hen doesn't need meds or antibiotics, use herbs and lots of good, healthy food to get her better; it's the BEST way for chickens. Mine is now almost fully feathered, her wounds have healed up remarkably well and all I used was the Turmeric powder after I had disenfected the wound area. The dog took a good gouge out of her back and she had deep incisor wounds under her wings but you would never know it to look at her now.
my dog killed one of my chickens "playing" with her while I was out of town last year, with some training and discipline he now ignores the girls, but it was very hard to go through. I hope that the rest of your chickies stay safe! 
