Poor thing. Coconut oil on the wound is the best natural antibiotic I have found. Although it looks like a spider, you know spiders can't actually bite, they need to be pressed against the skin for their fangs to puncture, usually through clothes or boots or pressing against a spider only then can they cause a bite. So a bite seems extremely unlikely to a chickens head.
I'm guessing she is scratching at the wound and agitating it, but even then it looks dry, but painful.
I personally would welcome a vets opinion but I would not let him touch it. It just looks like the type of wound to leave alone since there isn't anything really to clean or pus or blood or dirt etc. Just looks super painful and even necrotizing. Almost like a flesh eating bacteria, which is deadly.