I didn't see a rape. I did see Cersei protest at first...presumably from grief and also awareness of the location. And I wondered if she was finally going to end their icky relationship - but then if you watch carefully, she begins kissing him back even as she is saying "no", then she clutches at him (as opposed to pushing him away) and at one point she pulls him closer to her. She continues to pull at the fabric of his clothing, while he pulls at hers, and so it was indicative that she was getting into it. Gross? Certainly. Rapey? Not so much.
