A couple of days ago, we noticed one of our hens had all her tail feathers plucked out and bleeding. We separated her from the others, and I then noticed one of her wings was missing feathers and bleeding, and her comb was practically gone and bleeding. She's been better by herself, and this morning, I checked on her and noticed she is lethargic and not eating. She is scratching around the ground and "eating" the ground pretty much. I don't know what to do!! Should I change her food or give her any antibiotics? I'm new to this and want to take care of her. I've checked the other hens and she is the only one with missing feathers. Any advice??