It could be a head pecker from the sounds of it, I'd guess that before I guessed a predator, especially since neither sounds like a substantially grave wound.
What's changed in the flock recently? Have they increased egg production a lot, or have you added new birds for instance? If she's...
Are you sure there's no chance of injury... Not even a nip from a hen?
Sounds like a pretty normal comb injury to me, if it isn't, can you try and get a picture?
I know you posted it last night, but when in doubt with boys and cold, vaseline their combs and wattles. In this case, I'd...