Likely what happened is her head was grabbed, she struggled, he was too rough or both, which tore the skin. That could be it, or it was torn and others pecked at the wound and enlarged it.Thankfully her eyes seem fine. She can open them both, but the tissue around the left one is a bit swollen and that eye was closed when I initially found her. The rooster is a fairly young Welsummer, and his spurs haven't even developed yet. I have seen him mount the other hens, but not her. I haven't observed any aggressive behavior, so I was shocked to find the blood on the back of his legs. Of course I wasn't there when the incident happened, so I can't say for sure it was him, but I'm not sure what else could have happened.
I never give my birds pain meds. Personal choice for me, I'm just too nervous to give them too much. I give them some egg yolk if they're eating on their own and just keep them comfortable.