A hen that is high in the pecking will peck on the head to let the other chickens know to back off.
This looks more like feather pecking and is maybe a stress problem (too little space and hiding places) or maybe caused by unbalanced feed.
I would seperate the pecker so the other two can heal and look for some info about required space.
General advice for stressless chickens: 4m2 run space each for normal sized chickens, from sunrise till roost time. Free ranging a few hours each days helps but is probably not enough since the omlet coop and run are rather small.
Please tell us more about the space /lock up time and the feed they get If you like further help.