I raised all nine of my chickens from babies. they have always lived together. I went out this evening to check on them and I found one was missing over half her tail feathers and over half its feather around her neck. I stood there and watched for about 5 minutes and found that two of my other hens were pecking and pulling out her feathers. I have removed her for the nite. What could have caused the change in behavior? Also once I get her healed up will I ever be able to put her back in with the rest of my hens?