Exactly like Khane said, she's feeding you what she thinks you want to hear. From what you've said so far (I realize we only have your side to go on), this girl loves to display her "properness". Let me guess, she's always wanted a man with a "good heart", right? She's someone conscious of how people perceive her and her reputation. Biology trumps conviction ? sexuality, for as much as we think we can, will not go unexpressed. Celibate monks, moralistic republican senators, and the " pure", virtuous girl you?ve got oneitis for all want to get off, and they'll find a way to do so.
One of the trappings of a woman a guy perceives as a "good girl" is that he'll have a tendency to pedestalize her by default. White knights are a given, but even "PUAs" are prone to want to read more into the personality of a "good girl". A cute-ish "good girl" is a recipe for oneitis, because she seems to be above seduction. "I just want a guy with a good heart" sounds so fairytale perfect and with just the right amount of naivete applied, she comes off as a girl who truly believes Disney wishes really do come true. Even to guys with game, she appears as a "diamond in the rough" amongst the bitch-shielded women that populate the new hook-up paradigm. To chumpish white knights, she's an archetype ? the innocent damsel who needs to be saved from the world before it corrupts her soul and she turns into all the other women who wont date them. Both of them are equally shocked when she spontaneously fucks an alpha tour manager.
If you haven't done so yet, I highly recommend adding
The Art of Seductionby Robert Greene to your reading list. He begins by profiling the archetypes of seducers and amongst them, we find that our "good girl" is really The Natural; a child like innocence that masks a seductive motive. You may be inclined to think of a good girl as a prude, but this is often in error. The good girl needs to be seductively cute enough to make her hypergamy work for her. Any prudishness is reserved for putting a suitor into stasis long enough to evaluate better options, or in the case of your girl, the option to capitalize on an immediate Alpha experience.
The good girl's game is built around playing to the "quality woman" mythos that men harbor. They want to believe she exists amongst a sea of vapid, self-absorbed sluts, looking to cash in before they hit the wall. She's not the prudish Madonna and she's not the Whore of Babylon, she's the cute "good girl" somewhere in between. She's typically only a 7-8, not the vaunted 9+, so she also emanates a tantalizing potential of attainability. All of this makes for a very idealized, very cemented form of oneitis.
Just like all men have some form of game, women have their own game.