To BBIB, have your aunt watch the documentary "For the Bible Tells Me So". It thoroughly gives the points of view of religious people who have come around to accepting gays after seeing how much their intolerance has ruined lives.

And as always, fight Bible WITH Bible. Newsweek had a great article that details the religious justifications FOR gay marriage.

http://www.newsweek.com/id/172653

Cheers!