from there you can see how they do it. It looked like a kind of saddle to me, but a bike seat makes more sense. It's attached to the stairs. She doesn't levitate for that long, and after she's down Adam, who's mopping the floor, comes behind her and the seat falls into his bucket.
I'm pretty sure this is the same method they use for lifting Barbara earlier in the act, although I think that happens somewhere else in the set (?)