Grey Area Routine:
She let on that she had just come out of over three years of relationships
and had honestly never actually "dated". This explained a lot about her
behavior during the night, including her prudish behavior.

Me: "You seem like a very 'all or nothing' kind of girl."HB:
"Yeah, I guess that's how I've always been."
Me: "I used to be like that. I dated a girl for three years, but since webroke up, I've just been living in the grey-area."
HB: "What's that?"
Me: *Raises hand at about neck level* "If you think about relationships, and you say up here is a long-term relationship, with full commitment." *Puts other hand about a foot below the top hand* "...and down here is just a one night stand, absolutely no emotional involvement at all. Well, this area in between the two..." *pointing to area between hands* "...is a grey-area full of all sorts of interactions and relationships that two people can have. They can be just as fun or as fulfilling as either of the extremes, both people just have to be honest about their expectations."
HB: (they always say something like this) "I've never thought of it that way."
Me: "Yeah, and you can even move back and forth in this area as the relationship evolves."
HB: "I like it."
Me: "I do too. I think it's perfect for people our age, and in our position."
HB: "I guess I'll just have to be honest with you."
This sets expectations -- she knows you'll care about her even if you aren't fully committed to her. It will ease her as to what you expect from her, and it'll even DHV you because it's such a fucking clever way to look at the whole damn mess.