Keep her isolated with that bad of an injury. If they peck her skull when exposed they can do brain damage if thats wasnt already done. Plus you could end up with a others trying to eat her exposed flesh and cause even more issues. I have a hen that got a nasty wound on her neck but the others dont mess with it because it doesnt have blood on it and its covered with feathers. But chickens can be attracted to red so that could be a problem i would say use blue..what that ointment called anyways it makes the wound blue instead of red with a mild injury i would use that in this case i say she need to be in a cage you can keep her in the cage in the coop so she still part of the flock but cant get attacked by the others as she heal.
Hi the stuff is called bluekote. Beekissed on the forums here also has a recipe that I made up with oil and sulphur.
One of my young (about 4 months old as well) BCM pullets last year was severely pecked down to the bone on the top of her head. I put her in a dog crate and kept her in the house for about 4 weeks - plastered the cream on the head after gently cleaning it. I gave her water through a dropper and then some scrambled eggs and probiotic yoghurt and thought she was a goner the first 3 days. then she slowly turned around and even layed her first egg in our house.
she has a thick white scar on the top of her head but is a fully functioning member of the flock now.
So good luck and hope she improves!