Doppleganger again or something more sinister?

Yesterday morning,around 2:30-3:00, I was laying in bed awake, I could not sleep after waking up at 2:30am. We leave our bedroom door open just a crack so we are able to listen out for our daughters in their room. I was lying there in bed,looking out through the crack and I notice what looked like my oldest daughter coming over to our bedroom door,looking in and turning around and walking back towards their bedroom. I heard no noise, our floors creak when someone walks on them and I asked what she wanted. I got no response and she disappeared from view. I asked her about this the next day and she said she woke up around 2:30 that morning for a little, but did not get out of bed for anything and went back to sleep minutes after. I drilled her with questioning, trying to rationalize this for me and she insisted efactically that is was not her and that she did not get out of bed at all. My belief is that it was a doppleganger once again or something more sinster. Either way, this sorta freaks me out and has me wondering, how many times has this happened before, does it happen nightly and if I see someone, is it really them.