Hey M. - in all probability she's doing this because she can.
My girls both did this. It was a phase - granted a frustrating phase. The "discovery" of a new skill and the control it gives is pretty much what this is about.
My girls sleep pretty hard, so I would usually just make sure they had diapers on. If it was cold, I tried to get them back in their jammies. My girls also did this at nap time.
Maybe you can gently remind her that it's cold at night. Give her clothes in the morning (or let her choose her own) and attempt to put them on. If you can side track her with getting dressed instead of stripping off, that usually works - well, it did with the girls!
Unfortunately, it's a control issue - don't react to her taking her clothes off. Just act like it's normal and it also will loose some appeal - not much, but some.
She will out grow it - it just takes time.