My daughter does it. She's 4 and now she puts on fashion shows for us and company. The problem is she doesn't actually do the changing backstage -- she just throws a pile of dresses down in the middle of the living room and starts changing.
You said you'd been teaching her social norms for 2 years. I doubt that any of it is really sinking in yet. A two year old doesn't really adhere to norms ... even if they can repeat those rules back to you. Infants and toddlers are true hedonists. If it feels good do it ...
Hell, my daughter is now getting to the point where she practically says she "doesn't care" about our rules.
True innocence doesn't last long does it?
(Sorry about all the edits).