Talk about sex. It's a topic that interests just about anyone, and if she reacts poorly to it then she has a bad relationship with it or isn't mature enough for it, and you won't be getting much from her so you can move on. You don't need to go into gory details but mentioning light things (I hear so and so slept with so and so) can start it up. Believe it or not, girls are interested and like to talk about sex.

Talking about sex also reminds her that you are indeed a MAN with fully functional cock and balls. Do you know why girls say "I couldn't imagine being in a relationship/having sex with him?" Because they haven't imagined you as a man with masculine characteristics and an appetite for sex.

But the way you bring it up has to be smooth and natural. People have a way or mirroring the emotions of someone who says something. If you bring up sex in a nervous, awkward way, she'll assume that's how you'll be when it comes to it and that door will shut forever. So be sure you're comfortable with what you say.