Well, the key would be moderation, not absolute forbiddance. You can tell her that that kind of dancing will not get you respect by legitimate dancers, and that it is just silly.
Sometimes making something uncool is easier than saying "No!". (Forbidden things are sometimes cool just for being forbidden).
I know, not an easy line to....dance!
(BTW, just so you know, my little excised quote was not THAT bad, it just was not appropriate for a public kids party! Don't let your imagination get TOO active there!!!
)