Isn't it her night self? The one who sleepwalks every night. The story is hinting at it with Gowun "lying". No one entered the room from outside, she was already there and he can't tell her cause the adults decided to keep it a secret to try to not make things worse or make her feel bad.
oh lol i forgot she sleep walks thanks
So it's like she's replying to herself?
Yeah. It would make sense because the princess planned a meeting of other noble girls her age when she learned the other person was a noble girl around her age. And was excited saying they would finally meet but the reply was questioning on how that would happen.
I could be wrong though ╮(￣▽￣)╭
But does she actually make friends her age? And since we know does the princess other self tell her?
so who's the girl? is it a ghost?