Aloha Tenmore, It is indeed an injury. The problem with chickens is, once there is an injury, the other chickens will peck at it. If this is from a rooster you have too many for your flock of hens. If you have only one rooster, this is probably something else.
Could she have caught it on a piece of wire? Does she ( and the entire flock) have mites or parasites and she has scratched herself until she made a sore? It is important to find the source so this doesn't happen again.
As for this sweet girl, I would separate her and use a little hydrogen peroxide or aloe vera (avoid eyes!) on the wound. It will heal pretty quickly. Make an infirmary (you will need one for this and that over time anyway) in a cage that is free of drafts and out of sun and heat. Give her lots of clean water, grain, and fresh greens. She'll be fine soon.