I don't know if it's available where you are (I'm in the UK) but I had great results with a really stinky anti-pecking spray called Ukadex. It's so vile it almost made me puke each time I sprayed it but it did the job almost instantly. I would remove the worst bully from the coop and put the other one behind wire mesh so she's confined to a corner of the coop. I would carefully wash and dry the pecked bird so that any scent or colour of blood is removed, and then return her to the coop. I'd keep the bullies away/confined for a couple of days.Then before you put them back in, spray the bullied bird with an anti-peck spray. (Just on the pecked bits, cause it's not very nice for the bird to be covered with it when they're preening themself.) Watch them all for a couple of hours and if the bullies try anything, chase them off immediately. Hopefully that should sort out your problem.