I don't think Brenda is Rachel because if Aris really loved Rachel so much he would have been like ZOMG RACHEL when he saw her and he wasn't, so...I think Brenda is really Brenda. I think she probably is part of WICKED, or at least teamed up with them after they got rescued or something, but I also really don't like Teresa. At all.
I think they just told them they have the flare so they'll cooperate and they don't really have it. Really want to read The Death Cure likenaow so I can find out what's going on.