My sister sleeps with her head on the wrong side of the bed

It’s not like a huge thing to most people but it’s really annoying me and I have to mention it now so here I am. My (F32) sister (F23) recently moved in with me and she is sleeping in my guest room. This is all fine and I’m happy to have her, but she sleeps on the wrong side of the bed and it bothers me. My sister moved her stuff in and everything was fine, but when I went to take out the trash one night I noticed she is sleeping on the wrong side of the bed. She’s sleeping on the side closest to the door, but one of the two sides of the bed is against a wall and the other is against the window, and she’s sleeping next to the window instead of against the wall. It’s really been bothering me and I don’t know what the etiquette is for telling someone how to sleep in a bed you provided for them. Should I say something? How would I bring it up?