After considering it; I think that Rory develops hypersexuality once she starts to live in more populated areas and had access to more sexual experiences. As a kid, her parents REPEATEDLY hammered into her head that sex was bad unless it was for procreation, hiding any mentions of it from her and her brother.
So when she has sex for the first time, it becomes an act of rebellion for her. Even though her parents are dead, she still feels the need to rebel against their ideals. It becomes an addiction, a need to lash out against the ideas that sex is an inherently bad thing. Inadvertently though, as it becomes an obsession, it becomes a bad thing. At least for Rory.













