I think the picture changes with your more complete information on your daughter. I was concerned about a kid wanting an audition program with only two years of piano and thought it might even be good to redirect her
With voice as her primary instrument, and music a bigger part of her life than initially conveyed, I would say try to find a way for her to feel motivated, herself, to continue. And maybe a break is a good idea, to refresh.
I have another question. I really don’t know the answer myself. Is music education the best or only path for a vocalist who wants to lead choirs?
Would your daughter be interested in doing vocal performance alone for undergrad years, then seeing what comes next later? Is she thinking of BME mainly because of career concerns?
I would also ask if she wants a BM/conservatory/music school or would prefer a BA program (non-audition mostly). Talented musicians do go both routes. A BA program could include lessons on or off campus (often for credit and funded by the school) and performance in extracurriculars or off campus. A music major includes theory, aural skills, composition, music history, ethnomusicology, technology and so on and can provide a background for grad school. Some students continue to study voice or an instrument without majoring in music at all, with access to the right resources, and then go on to grad school or performance.
Most art forms have boring technical training and humps of frustration to get through. I recently took a series of art classes that was so fun- no technique, and we could do what we wanted. The teacher is now reining it in and we are focusing on drawing, perspective and so on, and I had the fleeting idea I would quit! Dance students often resist ballet as their “foundation.”
Your daughter is probably too young to decide on a career at this point. That can go two ways. She can move ahead with an open attitude about what she wants to do for school and work (and worrying about work can come later, it really can), and leave her piano lessons. If she reverts to music ambitions, especially choir director, she will play catch up the way other posters here have described.
If she has a genuine, mature, well-tested ambition to lead choirs, then piano will certainly be needed, and it would be easier to do it now, but she can, again, try to gain those skills later. Most schools have remedial piano so to speak.
Someone mentioned St. Olaf. That is a very flexible and quality option. The BA and BM both offer teaching credential preparation. Students often enter as BA students and then transition. It looks very flexible. Many double major. And they have a choral music program for undergrads. http://wp.stolaf.edu/musicadm/
Finally, you may have seen this: many find it clarifying over time.
http://www.peabody.jhu.edu/conservatory/admissions/tips/doubledegree.html