I agree with you 100% OP.
She is slipping, could be the start of a really serious downward spiral. 3.2 GPA? Totally unacceptable. Sounds like she needs a firm hand. I would cut her off completely from everything and everyone she likes...don't stop with socializing with her classmates, get her out of all activities (no matter how relatively harmless they may seem, they are probably going to eventually get in the way of her realizing her potential). After all, her potential is EVERYTHING. Now is not the time to be a kid...sheesh, her test scores show she is smart enough to know that. Remember, you may have to keep switching her schools when she gets comfortable and makes friends again. No big deal, though. So what if she resents you and becomes miserable, you are doing this to help her live up to her potential.
But, while you are at it...perhaps now is the time to think about your example. Are YOU living up to your potential? I mean, you may be doing well...but could you be doing even better? If so, then you really are not living up to your potential. If you aren't, why is that?