I personally think that academics should be a challenge at EVERY level. Don't get me wrong, she shouldn't be panicking over getting into her chosen college just yet. But I see the brain as a muscle - if you use it, it gets stronger. If you don't, it atrophies. If I were in your shoes (and please keep in mind that I"m not - you know your child, I don't) I would keep her in the new class. I think I would wonder about the fact that she didn't qualify for GT, though - if she's advanced enough to skip a grade, I see no reason why she shouldn't be advanced enough for GT. Maybe talk to her, see if there was something going on the day of the test, and if possible, talk to the teacher about it as well. Still, even if she isn't in GT, at least she will have class work that is a bit more challenging for her.
As far as the social issue, why not set up regular events on weekends when she can play with her old friends? Invite them over for a slumber party, or take them out for a picnic or something.
