Well, one of the two barred rocks has a real problem with the new girl, Cinnamon. We have the new bird in a run right next to the existing flock. They can see each other and the new bird tries hard to follow the other birds around, but if she gets too close to the fencing, one of the rocks tries to peck her.
We let them all out of the runs to free range in the back yard, supervised, and the rocks ignored the new bird for the most part. That is, until she got too close and then one of them would chase her away.
Our plan is to slowly increase the amount of time they free range together and also give her some time in the coop/run alone so she can find her way around. Eventually we'll try to slip the new girl onto the roost at night. But it may take a while before we get there.