I feel like the best way to combat this is to get in out on the table before hand, to have this conversation outside of the bedroom – while on a date, maybe even on the phone. Sort of have the topic of sex come up naturally in a conversation, don’t force it in there out of nowhere, but squeeze it in there somehow. Then, when she says she thinks it’s best to wait, be perfectly fine with it, agree with her completely, and continue to talk to her and see her. Then, the next time you’re with her, go for it and she may just give in.
I don’t know, that’s just my take on it, as it’s an issue I seem to encounter a lot.