So, prove her wrong by being an upstanding and dependable guy. One of her fears may be that as soon as you have sex, she won't be able to rely on you anymore because you would have gotten what you wanted. If your girl is going to trust you enough to have sex with you, whether it's her first time or if she's had sex before, then she has to feel like she can depend on you.
If you want to make your girlfriend want to have sex with you, then you should show her what an amazingly dependable guy you are.
