Re: Is their a Chook doctor in the house?
Do you have enough space in the chicken house. Sometimes, if they are over crowded, they will attach each other. Also, put a red light inside the house at night. (Full grown hens should have about 5 sf for each bird. You didn't mention the age of your chooks.....
Do you have a product called Blue Kote? You can purchase it where you buy your feed. The injured hen should be treated as soon as possible. They sometimes will peck themselves at the injured site. The Blue Kote will cover the area and will speed up healing. Some folks also put heavy black oil on chicken injuries. I prefer the former, since it's made for wounds. I would also put her on an antibiotic, which can be purchased at your feed store. Another good thing would be to add an electrolyte to her drinking water. Make sure she's drinking really good.
Good Luck! I hope your little injured hen will be OK.