It seems that one driver for the upper level girls may be the chance to compete in NCAA gymnastics, with perhaps the added lure of a college scholarship. About half of the graduating Level 10 girls (that is, apparently, about one for every 70 or so of those cute Level 5 girls) go on to compete in college, while graduating Level 9 girls who move on to compete in NCAA gymnastics may be numbered in single digits. If your child hopes to compete in the NCAA, becoming an 'event specialist' in Level 7 or 8 doesn’t seem like the best choice.
OTOH, if your dd doesn’t dream of such glory (or, really, even if she does) it’s quite possible to thoroughly enjoy a sport for years without committing the long hours necessary to achieve mastery—most golfers can attest to that. I had a great time in Little League baseball, although my fastball didn’t phase even my diminutive competitors, and I enjoyed football although my role as a kick-off and punt returner was such a life-or-death experience that it was clear that I’d never survive a collegiate program. I was a competitive cyclist into my thirties, even as I became increasingly (and, I suppose, rather pathetically) unable to fend off young whippersnappers in a sprint. I really enjoyed all that. It’s wonderful that some athletes can be great, but it’s great to be an athlete, whether or not you are a great athlete.
FWIW, my dd, like yours, is wondering how gymnastics will fit into her high school experience, and I don’t know what my eighth-grader will decide. Kids make different and interesting choices. Whether your daughter chooses to prioritize gymnastics or chooses to move on, I suspect that you’ll still think that she’s a great kid—and I suspect that you’ll be right.