Either way, they're just sorting out the pecking order. If this isn't a reoccuring thing then she's learned her place in the pecking order and they'll be fine. If they start fighting full scale and drawing blood then you have a problem on your hands. Even if they fight it might be good for them to establish dominance, only if blood occurs seperate. I've seen hens peck eachother on the head and peck eachothers eyes, it doesn't neccesarily mean gender and isn't that big of a deal. If this is one incident, it doesn't meat the standard of bullying either, which is a recurring problem and can really only occur in people in my opinion.