All good points, but I'm especially interested in 3 and 4. Those of us who are parents (and probably everyone else) are familiar with the term "teachable moment" -- this is one of those. As a dance writer, I would want to see this show highlight all kinds of dance, and all levels of engagement, from highly skilled professionals in all styles to avocational, once a week participants. I won't indulge in my full soapbox speech here, but we all know how significant this art form is, and how shallow her comments were. Alongside my distress as a part of the dance community, I was astonished at her willingness to make such cruel comments in order to curry favor with her viewers. That sticks in my throat fully as much as her nitwittery about dance.
If this child was excited about a math class, would she have quipped that "we all know how long that will last"?
And as far as your own query -- she wasn't thinking. That's the problem.