Okay, right here and now - this is half a control issue, and half a moral dilemma. First of all, I think waiting for marriage to have sex is dumb, but that is a personal preference. Is someone else wants to, including your girlfriend, you can't force them into it, morally speaking.
Now you can try to talk to her about it, but honestly if she's basing her decision on religious foundation, she probably will not change. That's okay. Just make it clear to her that if she won't change, something you're alright with, you must pursue someone else who is more compatible. It's entirely fair.
You can't force her into it, but waiting doesn't make sense if you don't want to. A relationship is a two way street, both of your needs should be met, so if it's not working with her, find someone with whom it will work.
