Conclusion
I spoke at length with Maria, and I explained that there was, first of all, no reason to feel guilty. After all, it was just an unfortunate fact that one of her early sexual encounters had proven to be unusually exciting-and of what would normally be considered a "perverse" nature. I don't actually believe in this concept of perverse actions in sex at all, and I used it as the term which would be familiar to her.
I explained that certainly, with time, and with definite efforts on Maria's part to explore-volitionally-other facets of heterosexual relating, her obsession could be alleviated.
I succeeded in building Maria's initial confidence in herself, and, ultimately, in helping her to overcome her obsessive-compulsive behavior by healthy sexual experimentation.