When we meet the girl in The Hitchhiking Game, she is timid, awkward, and easily embarrassed. How does she change?

Over the course of the story, the couple engages in role play, and for whatever reason, the girl is swept away by the role she plays. As the "hitchhiker", she loses her inhibitions and quickly leaves her timid self behind..... she's sensual, even forward. Unfortunately, her boyfriend is disturbed by the fact she has become like every other girl he has been with..... she is no longer special.