Her broody behavior may actually be encouraging that. Broody hens act in a distinct way when they're off the nest - they act more fierce and aggressive. It's a defense mechanism to protect the nest by convincing everyone that she's big and tough and not to be messed with. Often hens higher on the pecking order don't appreciate this and will go after them a bit to assert their dominance. I recently had to break a broody because she was just being too aggressive and starting fights with everyone when she was off the nest. As soon as she wasn't broody any more, everything was back to normal. If however they are all being very aggressive and really harassing her and you don't think that's the cause, you could always try pinless peepers.