I wouldn't think of making a joke of something so serious and tragic. Unfortunately, I don't know of any way you could prevent something of that nature, especially if it's part of their culture. Speaking of which, do you mind if I ask what culture this is in particular? I know there are several cultures in which arranged marriages are commonplace... As much as we may not agree with their traditions and cultures, often these things are not only culturally based but legally enforced. If there are laws in place to protect such arrangements, then there is really very little you or she can do to interrupt it. If the arranged husband-to-be is this resistant to the idea, even though the woman has made it so very clear that she does not love him or wish to be with him, then I see precious few alternatives.
Again, I don't know what country or culture she and her family are part of specifically, but perhaps the government could be involved somehow? I know the government isn't always the most helpful, but perhaps citizenship could be called into play somehow? I'm not the most knowledgeable about international law, but if the situation is that desperate I imagine your friends would be more than willing to look into it. Then of course there's the problem with the family, the father with the heart condition who so wants this arrangement to go through as he planned; I can't think of any way to bypass that, even with a heartfelt plea for a release. That one's up to the family to realize that love cannot be arranged by a third party, and to realize that their daughter will be very unhappy in such a relationship.
I'm sorry I can't offer more help, but it's a start at least.