As it turns out, the dancer in question, Mina Nishimura, isn't that new. She's invested in NYC's downtown scene, so doing something on live TV with a major pop star is totally unusual for her. But you'd never know, (nor would you know she had very minimal rehearsal time before the performance) thanks to her emotionally-charged dancing.
Nishimura is a trained Butoh dancer who uses the Japanese form to create her own contemporary work. She's weird and wonderful, so it's no surprise that Sia would want to work with her.
Does this mean that someday we might see Ziegler and Nishimura onstage together? With Sia calling the shots, it doesn't seem totally impossible.