Hello, I'd be very careful with the one that pecking her and causing that much harm to her. If it continues the chick can get depressed and die. If it continues then just seperate the one thats doing the damage for 3-4 days ALONE and then introduce the chicken she's bullying. At that point she'd...
I'd advice against that especially if it has pain killers in it. Damaged combs heal fairly quickly and isn't a major problem to deal with since this wound is severe this product would cause more harm than good especially if your applying it to an open wound. It'd also stain everything and burn...
Looks like she got into a fight with the other chickens. Please try and forcefeed her. Put an antibiotic cream on the beak such as neosporin (easily available) how many chickens and cockerels do you have in one place?