my DD did that too at the same age, she was toilet trained though ! she is 4 now and still likes to strip off ! but it is usually just her top these days

the only advice i can tell you is someone suggested to me when you put her nappy on to put another one on backwards so she has to reach back and undo the tabs from the back first before undoing the front, might give you a bit of time to catch her in the act and try and stop her.