He should offer to eat her puss after he's done with her. My wife liked that and would eagerly offer me her creampie. Of course she also urged me to suck his cock till it was clean after he pulled out. She got off by watching me suck her boyfriends black cock.
I also enjoyed her on top of my face while he fucked her from behind as she got a tongue on her clit and a cock in her. ANd I liked all the juices that would run down into my mouth.