Maybe Leia comes to visit Luke on his island now that Rey is there. And Luke and Leia are incredibly affectionate with each other around Rey. Kissing caressing etc. Rey doesn't realize it might be inappropriate at all because she's never seen a sibling relationship at all.

+ if maybe they even start having sex in the same room (think how everyone used to live in one room and it was normal(op is assuming it was normal??))
++ if Rey actually thinks Leia's moans are actually calming enough to fall asleep too.

Doesn't have to go any where as far as leia/luke/rey. But op doesn't mind if it does.