If nothing has changed since I saw it a few months ago, she is wearing an inflatable suit (like a track suit) and she rolls offstage, you hear the explosion and then giant chunks of what are supposed to be entrails I assume come flying out from the wings. Its not gross, they look more like ribbons. Then her dad comes on stage covered in them in shock and the interaction between him and Wonka just staring at each other is pretty funny for several beats.