Unfortunately you're on to a loser either way.
Option 1 - she stays a witness and either gets DF'd - in which case you'll be resented by her and her family for ever more - or marries you and becomes, in their eyes, 'unevenly yoked' - in which case you'll be resented by her and her family for ever more (spot the pattern?).
Option 2 - she moves in and gets DF'd and you'll be resented....well, you get the picture.
Life's too short for this - move on and find someone not screwed up by a cult.
Good luck.