I think that's a terrible attitude. Does she feel that a child who isn't a genius in pre-school should not move onto kindergarten?
What is important is that the child enjoys the activity. Somebody else mentioned the other benefits of a ballet class such as exercise, balance, learning discipline, socialization, ect. Even if a child isn't a natural talent, they will still learn and improve by taking the classes. Unfortunately, as kids get older, many dance classes and sports become all about how well the activity is performed instead of enjoying playing or performing it. Kids who aren't stars tend to drop out (or be cut) from teams and dance classes, thus losing all the other benefits of the sports or dance classes. When I was a kid, my parents found this great gymnastics studio. They were focused on fitness instead of just practicing for some performance (and charging the parents a fortune to see it). I remember seeing improvements in my fitness. For example, when I first started, I could not do a hip pull-up or even come close. A few months later, I was doing them with ease. It wasn't a competition with anyone else in the class (new students came in all the time, thus there were different levels), thus no 'stars' and everybody who stuck with it saw improvements and thus made the class more enjoyable.