K.H.
My 2 1/2 year old daughter does the same thing, so she always has to wear shorts with a nightgown, under dresses, etc. The biggest help, though, was getting her a couple pairs of tights. They are rather difficult to remove. Other than that, laugh it off, and definitely get her a potty chair. When my oldest daughter did it (around the same age), I told her that whenever she took her diaper off it meant that she should try to go potty. Eventually it became a game to her and she potty trained herself. Good luck!