Hello there,
You need to talk to her the days she is at the Livingroom instead of at the bedroom and ask her for the butt picture, you can also do the breast picture at the beach and use the oil. Do have in mind there is a choice when she asks you how you feel about her where you just stay being friends, so there's a chance you selected that one. You can also try reloading the game as it might just be a momentary bug.