As heartless as this may sound...... If you do decide that Bertha has finally become to much trouble for the flock, if you remove her completely by taking her where Percy can't see or hear her, Percy will recover in a couple of days.
Bullies don't stay in my flock. They cause too much stress...
They won't need to be sensitized to the peepers. The other hens knocking her down a peg will actually be good.
She will probably do some funny backing up and side stepping when you first put the peepers on her. Some of my hens have been pretty comical!
I blame feather picking, egg eating, cannibalism and long drawn out molts on the lack of animal based proteins in feeds. Since your husband objects to eggs being fed to them, buy them some dry cat food. They will love it! I use peepers on my grouchy hens.