Looking at the picture, I have to assume that she's moving backwards. Had she been moving forward on her previous steps, the skirt could not have gotten under her heel as it has.
Because she is, in all likelihood, moving backwards, the skirt will not be freed on her next step. Her ultimate predicament may not be so dire as falling down but dancing ON one's skirt, as Polished has pointed out, probably hinders one's execution.
I posted the picture simply to draw attention to the fact that, when dressing to go dancing, a lady should pay attention to the length and quality of her skirt.

jj