Are you doing the soaks and cleaning daily? Is she spending most of her time lying down or resting on a roost bar. Or is she getting up and walking around during the day? Breast blisters which can get infected with pus can be from lying on damp or soiled bedding and from a rough roost bar...
I am really sorry about your hen. Has the vet examined her? It is hard to say what may be wrong causing the scabbing. It could be a bacterial illness, but I think she needs the vet to help her.
I would soak her in warm water with Epsom salts, Betadine, or chlorhexidene for 15 minutes daily. When dry, apply some triple antibiotic ointment on the scabs. Is she was on damp bedding or ground, her skin was breaking down. Does she have any mites on her body now?