Iodine or BluKote may darken the skin well enough to hide the wound and prevent pecking. I would probably give it another try to slip it under the broody early in the am as PDR suggested. Stay close, and make sure she doesn't attack it. The feathers should grow back in quickly. If you cannot get the chick back with the broody, I would consider bringing in at least one or all of the chicks to a brooder. But broodies do such a better job of raising them. Chicks can get hurt if they get away from the broody, especially at first. I usually keep mine in a large dog crate for the first 3 days until mama is ready to take them out with her. Usually by then, she will kick some butt if the others come near her chicks. Good luck.