fivethirtyfive, is your daughter applying to BM or BA programs?
I would like to add that I know someone who didn’t take all the recommended classes for admission to Harvard (no senior year science, math to AP Statistics with no precalculus, that kind of thing) but got in due to participation in conservatory prep and a music seminar at a college (not for credit).
The discussion sometimes is around how conservatories care most about auditions, but some conservatories/schools of music are part of colleges or universities that DO care about academics. And on the other side, even elite schools will look favorably on a kid who does a lot of music but has a little less rigor in academics as a result. Music requires so much time and discipline and admissions folks know that.
Some kids are naturally talented in academics and don’t need all the AP classes to function well in college. In fact, in educated homes, reading skills go UP during summer break 
In other words, it is hard to generalize. I think kids who love history or English should take demanding courses if they can. Kids who don’t like academics are fine lightening the load. I wouldn’t worry about it too much but go with what the student wants and loves to do.
Then think about finding a school that fits the kid, rather than fitting the kid to schools.