Brother, you've got your hands full, and you haven't even gotten to first base!
But seriously... the person known as "Check_Your _Premises" offered some good advice:
Get her to think about OTHER cults.
Check out the movie that "C_Y_P" mentions in the thread he linked to, and try to rent a copy of "Ticket To Heaven" from your local video rental.
Keep telling her it's not about the Witnesses, and you're glad the witnesses aren't like that.
You may get ther to think.
You may lose her in the process.
But rejoice! For there are HOTTER chix than her to be had, and they don't have all those Bibles and Watchtower books in their luggage!
"Tis wise advice not to become unevenly yoked with one who is not your intellectual/philosophical equal. Life is too short.