Tricky one this.
Ignore her cr@p about waiting till marriage. Sounds like if your almost in there she wont wait anyhow, and if you respect it she'l only get round to doing it with some other bloke.
You do need to play this one strategic without upsetting her too much. Does she have any female friends that she talks to that like sex? if so, they will tell her how good it starts to feel and she will get curious and eventually go for it.
Best advice is to keep progressing things slowly until she loosens up to the idea. try to encourage her in a non pressured way about how its a natural thing to do, and after a bit its better than chocalate ha. oh and its great exercise too. Tell her stuff like you respect her for having values, and you think it will make your relationship stronger, and you will both feel closer together after.
you need to talk women talk to get her to put out the first time. after that its smooth sailing. go easy on her the first time, and yea stop doing everything she wants until you get some of what you want.
make sense? I hope she's worth all this effort my man.