I would try to let this go. Having sex in a risky place doesn't mean it was good sex and if she's telling you that it's good with you, accept it. I've always had issues with my boyfriend's sexual past but people are in different places in different times of their lives and what thrills them and makes them happy at one point in time isn't what makes them happy and fulfilled in another. Sometimes that "risky", or experimental stuff just gets overblown. Be happy where you are with her now.