We recent moved. For one week, my free range girls were kept in their run. The day we went out to move the coop, we found one girl missing feathers and bloody. We have separated her to give her time to heal. That started Dec 7. Finally has all her feathers and even laying. Tried to introduce her today and the flock attacked her. We had to jump in to get her out. Why are they doing this all of a sudden?
Are they back to being free range? Any time a bird is gone from the flock for a period of time, the other hens are going to force her to reassert her place. You may need to rig a "look but don't touch" set up for a while, and even then once she is back with them there will be some good squabbles. I let them sort things out unless there's a decent amount of blood, or one bird has clearly yielded and is simply getting pecked. Be sure they have plenty of space and a few hiding places.