(Where did you get the idea that the Rockettes were the best dancers in the world?)
Their training comes from millions of dance classes, all across the country.
There aren't too many places that allow open rehearsals. You might want to contact them directly -- but I would imagine they get hundreds if not thousands of these kind of requests.
The best things is just to get her to love herself in the dance and keep striving to learn.
If we're not having fun, then why are we doing it?
These are DISCUSSION boards, not mutual admiration boards. Discussion only occurs when we are willing to hear what others are thinking, regardless of whether it is alignment to our own thoughts.