I think she is old enough to have some say in the matter. (Assuming it's not just about staying with friends or thinking she'd lose face).
Two different scenarios to think through:
What if you exercise parental override, put her into the more challenging classes and she crashes and burns? Can she drop the classes, move into less challenging classes? Would this be highly unusual in her school? What if she continues to get Bs and Cs, would this be a problem? For whom? (Asking this coming from an educational culture in which people would keep their kid in the highest track possible no matter bad grades as long as the kid does not actually flunk out with Fs, rather than keeping children at a level they can make As).
What if you put her in the classes she's qualified for according to her grades and it turns out she is way under challenged? Can she move up? Does she lose the chance of a more advanced math track or similar for good?
Basically, which is the situation easiest to correct if things go pear shaped.
