Does she play another instrument? Will she audition on piano or something else?
Is she in a choir or does she admire a school choir director? Where did the BME and choir director ideas come from?
She must understand the importance of piano for any music study, including theory, and for what you say is her career goal at the moment. If she understands these things clearly, but wants to quit, then I would allow her to quit. She is getting near the age when she will be making many decisions on her own. She can end up applying to a university or liberal arts school and exploring majors her first two years. If she still wants music, all is not lost, she can major in music and do music education later. When she finds her own motivation, she will practice and stick with piano.
I have seen some negative scenarios in which a parent nagged about piano, some resulting in very talented students quitting as soon as they left home. Net result was end of piano, and a problem in the relationship between parent and child.
My own child started piano late when she became interested in music in late high school. She hated the method book type of lessons so the teacher gave her more interesting contemporary classical pieces to play. She was intrigued by theory and this teacher also geared lessons to that and to occasionally composing. I never suggested piano to her: she was the one nagging. She was barely proficient in piano during undergrad music major, which did make things hard. But she is now in a doctoral program in music- stuck with it!
You could offer help in finding a different teacher with a different approach, as others have said. A respected adult musician or director could talk to her about getting over the hump of frustration, if that appeals to her. But overall, I think, “developmentally,” motivation needs to come from her and she needs to show some eagerness.
I don’t know how long your daughter has had this career goal, which is pretty specific for her age. It is fine for her to stop thinking about career for a couple of years or more and explore. There are many ways to study music. It sounds like preparing for auditions could be stressful for her, unless she has been playing another instrument at a high level for awhile. She can major in music for a BA program without auditions.
And there are many interesting majors in college, obviously. They may not have a direct job application, in the vocational sense, but lead to opportunities in many fields and grad or professional schools.
I would encourage her to continue if she wants, tell her that at her age these decisions are hers to make, and also encourage broad exploration in late high school and early college, with no pressure to decide on a career right now. During college she can volunteer, intern or work and participate in extracurriculars that will help guide career aspirations.