I don't know blob, but I have a hen like that too, and I almost got rid of our rooster too. But I think our hen is starting to molt. How old are your hens?
Another one of our hens is losing tail feathers and neck feathers, and I think she's molting too. Otherwise, I do wonder if the one with the bald patch on her back might have mites. I'd rather it be molting than mites.