you just have to try to get more comfortable around her and in turn she will get more comfortable around you, and so opening up to you, here are some things i have found have worked for me in the past. Firstly try just not doing any sexual activity for a while, just hug and act as if you don't even want to do anything sexual with her, usually i believe the girl gets the impression that she has to prove something to you, and in my expierience has made her basically jump on me, secondly try the above and then try and hug her, kiss her gently then you should wrestle her down, pin her arms down aswell, this is usually a massive turn on for girls and she will be pretty open when she's horny, Lastly just give it time and when she finally does open up it will be alot better, girls usually holding back makes it better for us men as its much more satisfying is you wait for something, kinda like an orgasm, plus you don't want to get into a situation your not ready for and blow your load too early, luke