Yeah, 1 needs to consider a teacher switch as an option (especially since lw didn't actually say she'd asked to quit, just that she hates practicing and wants long nails.) The nail thing seems unreasonable for someone who's not really serious about piano as a career, but also age 12/4 years in is about where piano is going to transition from basic music lessons for kids to something different. If this teacher mostly teachers kids and beginners, they may not be right for someone at your kid's current level and she's bored because she's not feeling like she's learning much anymore; conversely they may be trying to transition her to a "career" track for people who take their playing more seriously than she ever wants or needs to, and she's feeling pressured to practice more intensely toward goals she doesn't even want.

I certainly feel like I spent my last year of lessons learning nothing except how much I hated rote-memorizing long but obscure classical pieces in order to perform them once. If I'd had a teacher who was either willing to teach other ways, or better able to explain why what I was doing was important as a foundation for other things, I might have stuck with it. I don't regret not memorizing more sonatas but I do wish I'd had a chance to learn things like chord theory and playing by ear and how to play in different styles for different genres and principles of fingering and how to accompany, or even what a sonata is, all things that would have served me better in adulthood than memorizing and immediately forgetting an uninteresting recital piece.

I'd check in with the teacher about what her aims are for older intermediate/advanced students and see if you can get that aligned better with your kid's interests and aims. And yes maybe look for voice lessons instead, or even a piano teacher who can focus on something like accompanying voice rather than classical recital or whatever it is she hates practicing.