One can try this or that - but really this behavior will drastically decrease your enjoyment of the flock. Hideouts are good, pin less peepers have worked wonders, and other ideas.
But the truth of the matter is sometimes you get a bird that just does not fit with this flock. Being raised together, really does not have much influence on adult behavior.
If you pull the bully, in a dog crate does the behavior stop, and the victim bird is accepted by the others? Sell the bully. But sometimes one can almost blame the victim. Sometimes pulling her out will restore peace to the flock. Generally it doesn't matter, just get rid of one of the birds. An aggressive bird will often fit better in someone else's flock.
Always solve for peace in the flock. And a funny thing is, is when there is a lot of this kind of turmoil, it upsets the birds that are not being attacked too.
Mrs K