My daughter did the same thing wrt not wanting to wear anything in bed. I put a nappy on after she was asleep until she was dry about five months later. Usually, around 11.30pm, there would be a thud as she removed the now wet nappy and hurled it across the room! She was dry for the rest of the night. Incidentally, over the course of about three weeks her nappy became dry all the time. Nothing else changed wrt fluid intake/toileting so I think she was just physiologically ready.