The game of volleyball changes when the girls become women, muscles appear and it gets more athletic. So between ninth and tenth grades (15s in club and earlier in the better programs) you see a lot more blocking, you have to hit over or through people, the velocities pick up, and the kids that can’t keep up are left behind. There’s not much in the way of skill that’s going to get a 5’6" OH to hit past a couple of skilled 5’10" blockers. For some it means a move from the front to the back row, and for others it means a move to the bench.
What’s common is that a high school roster is composed of two groups of kids: the ones who play at good clubs and the others. You can usually spot the ones who are playing year round, and the team will go as far as they carry it. The others will get scraps of playing time, do a lot of goofy cheering and have fun in practice. There are actually a few on my DD’s team who would rather not play in games because they don’t want to screw anything up, they just want a couple of early season appearances to get a letter and then go hang out and be on the team.
If she finds joy in being a teammate then celebrate that. If she’s not ready to face the end of her career yet, let her ride this out and come to grips with it later. As soon as this season ends, however, she’ll have to choose spring softball or club volleyball, so there’s not going to be a lot of time to mull it over. She already knows in her heart if she’s ever going to make varsity or play (and she’s probably right - the kids know who should be playing) so it’s just a matter of how comfortable she is with that path or another. For me, sitting on my hands is the hardest part of parenting. I’d suggest biting your tongue and watching to see if she’s enjoying how she’s spending her time. If it looks good then let it go. High school is hard without a tribe and sports can really provide that.
Also, consider that if you don’t like driving to the gym six days a week I am not sure how much you’re going to like driving to softball five days days a week plus spending the rest of your summer weekends at a suburban SB complex. And SB may not be any different as far as playing time. You only need a few pitchers and the coaches may never play the bench there either, especially given substitution rules that don’t allow putting the stars back in the game.