For the OP: I had a situation with one of mine that is sort of the reverse of your situation. I’d always wanted this kid to get involved with a terrific Boys Choir in our area. No interest. I mentioned it several times along with all the goodies he could partake in - choir trips to England, nice group of kids, etc. No go. I dropped it and didn’t insist since his plate really was full. Well, said kid has grown up and picked up some church organ work as a sideline. Boy, is he kicking himself for not taking advantage of the choral training in that childhood/adolescent opportunity. He’s now paying for voice lessons and looking into getting some choral conducting training. I sort of wish I’d driven him over to a boy’s choir rehearsal or two when he was a kid.
It is sometimes quite hard to know as a parent when to insist and when to let the kid take total responsibility for the decision. In an instance like yours where she is gaining basic skills that could be useful, I think I personally would more inclined to strongly encourage her to continue. If she goes the music route, she will never regret the time she spent on piano, but if she quits, she may regret she didn’t try harder before her college years. And, by her senior year, interests might be more defined and the situation can be reevaluated.
If it helps at all, it is very common for college music majors when required to take piano class or lessons to pass the proficiency requirements to find the course frustrating. They are proficient on their own instruments or voice, but suddenly at a beginner or barely better level on piano and it is discouraging to have to work hard for basic skills so far below their other musical accomplishments. I’ve also seen this with adult beginners who start up with great enthusiasm and commit lots of time to practice, but quite soon the learning slows down, skills come slower and they get discouraged and quit. She may be one of those who started out at a fast pace, but for whom this will slow down as the music becomes more difficult.