Thanks for the commiseration even if there isn't a solution
! More challenging classes aren't an option right now in that she's in the last grade offered at her middle school and is in the most advanced classes they offer in that grade. Further grade skipping isn't likely to be the best option as I'm not sure she needs it as she'll be a high school freshman next fall and I don't think that skipping part of high school is the answer right now.
I'm hoping that the classes in high school give her the opportunity to be challenged by the content more than the quantity. Middle school seemed challenging for a while but, in hindsight, I think that it was that they load them up with tons of homework (expected 2 hrs+/night) and speed is her weaknesses. Math is probably the only area where I can say that the content has been fairly sufficiently challenging.