Yup, that's been my experience. The only way I've seen a bully "reformed" is by rehoming her. In the new peck order, she starts out at the bottom of the peck order and does not have the confidence to bully anyone.
I know this won't help the present situation, but maybe will help someone in the future. Bullying usually begins with just one bully, but if left unchecked, other flock members may join in. The victim can be tormented endlessly and eventually killed. If you can intervene while there is still...