From what you're describing, it really kinda seems like this is hurting you more than it is her. Yes, it hurts to be left out and to have people who you think are your friends suddenly shift alliances. OTOH, if she has other parts of her life where she's happy and productive, this may just be one of those painful parts of being a kid that gets better as the other kids mature a bit. It would be more concerning if this was her whole world, but it sounds like it's just one piece of it. I'm not trying to minimize, just kind of speaking from experience. She sounds like a really terrific kid. I have a feeling she'll come through this OK. You're a good mom.