MomofAdult,
I disagree with your comment that practice is generally not “fun”. Practice might be frustrating at times and maybe not be going the way a student wants. But not “fun” makes it sound as though it is some sort of chore. And the musicians I know do not feel that way about practice. I agree with your comment about how hitting a plateau can be discouraging. Kids who are motivated to excel at music are often more motivated than ever to work through those plateaus in order to to get to the other side. Sometimes a new teacher, a new approach, even listening to a new type of music can help re-engage a student and help them over a plateau.
As for the original poster, I also think you have to be open to the fact that your child’s path might shift and alter. As a Junior in HS she is still figuring out who she is and who she wants to be. There are only so many hours in the day. You mention a dual-degree, teaching and other interests. She sounds as though she has a broad range of talents. I would not try to fit her into a box just yet but listen to her and allow her to be your guide. She might surprise you with where she ends up. A child who is leading a choir might become a team-leader in a business. She might become an arts advocate. She might become a creative working in television. Right now she might say she wants to be a teacher but these things change. Make sure she knows that there is a huge range of careers and jobs out there.
So one way to channel your helicopter-y inner parent is to open doors rather than close them. Maybe music education is to limiting. Maybe she needs to re-iginite her motivation by exploring new goals and new ideas.
FYI I work with parents who have kids who are struggling big-time. Often these kids have lost all motivation and have given up. One exercise I ask the parents to do is to think back to when their child was 7. Who was that 7 year old? What did you as the parent see them growing up to be? Who did they say they wanted to grow up to be? There you might find clues as to what to expose your child to or ways to reignite a passion that seems to be waning.