Rachel and to some extent Britney get bad edits on the shows. For example, they didn't show all of the first fight when Rachel came back, and they didn't show any of the hour when she and Ragan talked in the HOH, ending with hugs with each other. If BB hadn't wanted that message to be shown, they would have opened the mic in the HOH room and told her to stop it. They still could have removed it before Brendon came back into the room. I think it was for drama, buzz and ratings.
I'm not defending Rachel's overall actions, I do think in this case, she was used. There was no reason to bring her back into the house except for drama.