L.B.
My daughter did the same thing and I think it was just because she thought it was morning. So...I tried putting a nightlight on a timer that went off at the time she normally woke up in the morning. We call it her "magic lamp" and made it big deal about how special it was because it knew when it was morning and time to get up. There were a few times she still got up at night but it was much easier to get her back to bed because the magic lamp wasn't on yet. I hope this helps!! Good Luck!
L.