The main trick:
https://www.youtube.com/watch?v=goO7lKRdVX4


They also throw in a little flair with the Zigzag box trick to make people think that is the trick, but it is likely not associated with the trick at all. Magicians do fake look alikes to make people think they know how the trick was done, but it is not the actual trick but a decoy.
https://www.youtube.com/watch?v=Mcwm4MhOG5I



MY thoughts, there is a lot of room in the top as someone else pointed out. She probably is standing and arched across the top of the box with the hole going right beneath her. Her legs are likely standing on the 2 left corners, she is arched along the top of the box.


Ofcourse I could be wrong because they could easily have found a way to do it that is not what I am thinking.