In ''be part of something'', she smiles almost all of the time. I thought is was an ironic or secretive smile. But i was wrong. Bree is never coming back. Even if she does, she won't stay long. As Buffy in series 4, death is her gift.
Her whole life has been a lie, the people she loved as parents are dead or missing, her presence brings pain and danger, not only to the people around her, but also to innocent strangers. No matter how much she tries to avoid THEM they will always find her. It says it in LGpeadia, she surrendered. She is sacrificing herself to save the rest of the guys. That smile is the smile of someone who knows that the end is coming, but by it , her moral victory follows.
She let go.
She chose not to let THEM destroy any other girls life.THEY have already destroyed hers. There is nothing else for her here anymore....
'' Never look back '' she says, as in " don't worry about me..... i found my peace.... i am awakened..... ''
but.. i'm glad i'm not the only one thinking about this now!! 
TTFN!