If your roosting bar is six feet long, you've just got barely enough room for seven chickens to roost. This suggests to me you may be verging on over-crowding, and that can start a stress effect in the flock.
It would naturally manifest itself by the pecking order re-ordering itself to try to relieve some of the stress. Your Cream Legbar may be challenging the others, thus her disruptive behavior.
I would begin by figuring out how to increase their coop space. Three nests for seven hens is not necessary. You could get along with two.
I would watch them carefully at roosting time to see if there are any conflicts. Observe who is bullying whom. You just might find out that roosting time isn't as peaceful as you think.
If there is a lot of squabbling going on, you need to figure out how to introduce more perch space. I solved this problem myself by removing two unused nest boxes and building an additional perch. I've found that the more perches there are, the less conflict you'll have. It's far more important to have too much roosting space than too many nest boxes.
