"

 Dance Till You Die 

According to the summary:

""Taking over the stage, the witches perform a Broadway-esque musical number highlighting Midler's talent — and putting a spell on the adults to make them dance until they die.""

I thought she was just playing into Max's characterization of her as being the real sanderson sister. She didn't have the spell book with her, so how could she have casted a spell on the parents?"