My fiance's parents are blackmailing her not to marry me?

I can understand your frustration at the whole situation. I am not of any religion, so it is different, but for very different reasons I cut my family out of my life, a marriage cannot exist in harmony where the parents are in control of it, and if her loyalties lie more with them, and she cannot find the strength to put her own happiness with you first, it doesn't bode well. If she really wants to be your wife, she needs to make it clear to them, that however much she loves them, she has her own life and decisions to make, and if they cannot support her in that, they are not worthy of her, at 30 she is a mature woman, not a silly teenager who needs guidance to know her own mind. I was far happier without my family destroying my life, and i've never looked back. I hope it works out for you, maybe counselling for her could help her find the strength to follow her heart whatever the consequences x