At what age did your DD/DS stop using nappies at night?

My DD is 2.5 and although we think it is way too early to stop using nappies at night she gets into bed and pulls her nappy off and puts her pants back on. Only when she is asleep do I sneak back in and put it back on. She doesnt get up and go to the toilet immediately so I am not sure if she is wetting at night or in the morning on the days that she is wet.

She toilet trained at around 21 months (by herself). I know there is a big vary for the norm. I was just wondering.

TIA