There is nothing you can do. Either you are sexually attracted to someone and feel chemistry with them or you don't. She just does not feel that with you. I know it sucks, but it's not something you are doing "wrong." She thinks you're a great guy; she just doesn't feel any sexual chemistry with you. I've been in her situation before. I've gone on dates with people who are great, but the chemistry just isn't there. There is nothing the other person can do. Chemistry is just somethig that happens... or it doesn't. Unfortunately, you just have to move on and find someone you DO have sexual chemistry with.