Ngl I understand mc's mindset, it feels bad to play when there is no passion in the group and you're just the best one out of them by a mile. You'll get disinterested fast and won't enjoy playing, so you'll suck and your team will as well.
Even if there's an important competition in sigh, if you don't treat it as important, you'll just be wasting your time if you stay to compete in it.
I support her decision to quit, it was a wise one.
She could also have went for a more competitive club, but she wasn't that interested in volleyball anyway, so it's good.