I've got a similar size menagerie (including the patient husband), but have 8 Tennesee Walkers that rarely are ridden, plus two donkeys and cows including pet longhorns. Love all my pets!
Why don't you just keep her separate from the flock? May not be practical. Is there one or two other hens that get along with her. Perhaps you can keep them together.
I have the same problem, but do not have a rooster. Could another hen be pecking on one of my girls. In addition to the bald spot on her back directly behind her tail, she has a bald spot on her bottom. Any suggestions?