Simon:
Show us the official rules of your religion or shut up.
They'll simply state that it's in their Bible and it is. It would be best for us to show her the rules in the Bible that she wishes to ignore. Quote a bible verse that they definitely won't abide by like the one in Deuteronomy which states:
28 If a man happens to meet a virgin who is not pledged to be married and rapes her and they are discovered, 29 he shall pay her father fifty shekels of silver. He must marry the young woman, for he has violated her. He can never divorce her as long as he lives. Deuteronomy 22:28-29 New International Version
Once quoted she should be asked if she would give out a marriage license in such a case. When she says no ask her what gives her the authority to pick and choose which Bible verses she wants to abide with and which ones she doesn't. Accuse her of hypocrisy for not following the whole Bible.