Hi,
How long has your daughter had the chickens? Is the one you think is being bullied new to the others?
I have 8 chickens and they still argue at feeding times, I think its all to do with the pecking order. As long as she gets to eat and looks OK i wouldn't worry too much. If they peck her too much and starts bleeding then i would remove her until she is healed ( Sometimes chickens will keep pecking if they see blood). Then maybe try to introduce her to the others again.
I'm still learning too but I'm sure someone will be along and correct me if I'm wrong. ;D
Lucy x