My half blind hen was picked on as a chick and I did have to resort to using pine tar once to put a stop to the pecking. I also have a loner hen. She's been a loner her whole life.
I put my half blind hen on the roost at night, because she can't see to get up there by herself. I always set her next to my roo, cuz she's his favorite and he won't allow any picking on her. She's a scrappy little thing and has gotten more assertive as she's gotten older, so nobody really messes with her all that much.
My loner does her own thing. If she wants to hang out in the coop all day, I let her. If she wants to be out with the others, I let her do that. She is the only one that I allow to sleep on the boards between the nestboxes, where she's not picked on by the others at night.
I free range and that helps because there's always some place for a picked on one to retreat to. I try to interfere as little as possible in their pecking order issues, because most of the time they do work it out. In confinement it's not so easy. If it were me, I would focus on removing the one doing the most pecking - the pecker, not the peckee. A couple days in chicken jail can really knock them down a peg on the pecking order ladder.
Obviously if there is blood being drawn, the injured one needs to be seperated until healed, for their own safety.
I'm sorry I don't have more helpful hints to offer.
