When I was around that age I remember I started getting kinda bored with violin (I had only been playing for like 5 years at that point). Didn't want to practice, didn't really look forward to class, etc. My parents and music teacher made me stick with it, and eventually once we started playing better, more challenging pieces, I was really into it again. Looking back, I'm so glad they wouldn't let me quit.

It sounds shitty and she'll probably complain a lot at first, but honestly just lay down the law and tell her that she has to choose at least 1 "thing" to regularly be involved in. I think it's really important in the way of developing a sense of discipline, commitment, and work ethic. And music, acting, art, a sport, debate team, volunteering, or whatever are all things she can keep with her for the rest of her life. I'm 21 and still pick up the violin from time to time, and have also branched out into singing. It's awesome.

So in this case, I think making her do something she doesn't (initially) like is honestly a good thing in the long run. It seems like she's good at singing -- if she's shy about doing solos, then maybe have her join another choir outside of school, or branch out into musical theater? If you can afford it, maybe even private voice lessons to challenge and engage her a bit more. Middle school is a rough time and friend drama will eventually happen. I think she should have something additional in her life that brings her joy. Or maybe I'm just salty because my parents didn't have me start singing when I was younger :P