Once you initally take her out of diapers, I'd either lock the bathroom or find some way of keeping her from taking off her pants. A sure-fire way is one of those belts with the rivets used as belt holes that go all the way around, you can lock those easily, a piece of chain does in a pinch, but isn't near as comfortable. A simpler way is a piece of rope put through her belt loops and tied in the back, ends tucked into her pants. I can suggest some good knots if you don't know any.
Also, putting multiple, bulkier diapers on her will probably be more baby-ish.