We had a black hen that was menaced by two mean girl Leghorns, and of course the other hens followed their mean girl lead. They mostly lit into her back and pecked it raw, and she lost a great deal of feathers, I’m sure from stress as well. We put blue vetricyn on the wound, to cover it and make them not “see” it as well as open flesh. This helped. We also bought a sort of chicken saddle that she wore that protected her back, like a canvas shield. This also helped, a lot.
She was still being menaced, however. We have a small wire run attached to the coop. At night, we lock them in the coop, but they should be safe enough in the wire run. What we ended up doing was taking the two mean girls out of the coop every night after bedtime, closing it, and putting them on a roost in the wire pen.
We did this for, oh, a month maybe? And doing so really shifted the dynamics of the flock. The separation took the hens’ attitude down several notches, and the others gained confidence. When we were eventually able to take the black hen’s saddle off - she’d regrown her feathers and healed - we let the Leghorns back in the coop. No more problems.
Not saying this would be workable for you…but just an anecdotal account of an experiment that worked in our case.
