I went outside to check on the girls and noticed RJ's comb looked injured. I think maybe there may have been a tussle with one of the other girls and she got RJ's comb. Should I be worried about infection? How do you treat a comb injury?
It will probably heal on it's own since it appears to be a peck wound. I have had roosters' combs split and bleeding, and not treated them, mostly because I couldn't catch them. Since the bleeding has stopped, about the only thing I might do it to apply some iodine or Betadine to the scab.
Combs are not too prone to get infected. You could put some Neosporin on it and check it every day. I'm glad it scabbed over. Chickens can be tempted to keep pecking when they see bright red fresh blood. There is an antiseptic product sold at farm stores called Blu Kote that, as the name suggests, is blue and helps hide a fresh wound. You probably don't need it now that her comb is scabbed over, but is a good product to have on hand.