Aww, poor baby, we had this happen to one of ours, maybe not quite so severe. We brought her in and kept her in a cage in the house, cleaned he wound with warm soap and water and put triple antibiotic ointment on it, then left it alone. It turned black, and she wasn't too interested in eating or drinking, but as time went on, she got better. The 3rd day, after bringing her in, we gave her some of her favorite foods, grapes, applesauce, cooked oatmeal, olive oil, coconut oil, hard boiled egg. That got her eating. Sometimes we would take her cage out into the backyard for an hour or two for fresh air, once her wound looked as if it were closed and healing sufficiently. It took a long time a few months, but now she is fully recovered and has a new flock and laying eggs again. I never was able to reintroduce her to her original flock, so we got a couple of very young pullets, that were just beginning to feather, and let her sit next to there cage, and pen for weeks, until they were old enough to be together. Chickens are amazingly resilient.
you are a real trooper, and I'm sorry this happened. 
