I had the same problem. Very recently. I just posted pictures of her bald little head. I used a neosporin wound cleanser that is for kids. Had it on hand from my granddaughter. Then put neosporin ointment on her. Had to keep her separate until it healed. It's healed now, but shes bald. She's at the bottom of the totem pole. I have her in with the others again after a couple weeks. I still have a separate feed bowl for her. When I had her separate, she was so upset. After lots of help and advise from all these good people, I found her a buddy. One of the other bantams that I noticed was not one of the ones picking on her. I let them both out in the yard together to free range when I'm out there. Without her buddy, I couldn't do anything. She was right under my feet when I was trying to get some gardening done. I was bent over with the hoe and next thing I knew, she was on my back trying to get up on my shoulder.
Someone told me to use the bluecoat also, but I haven't found it. I just kept her separate till she healed.