In a practical sense, this will end one of three ways. One, the most desirable but unfortunately the least likely, the grandparents cede and let the issue drop. Two, the most likely 'good' outcome, she puts up with being disowned by them and backs out on her own. It'll hurt her and her parents, but that's not on her head, that's on her grandparents. It doesn't matter what their motivations or beliefs in this matter are, they are still in the wrong by a long shot, and any harm they cause as a result of their actions is just that, harm THEY cause. She should pursue this option as soon as possible, the longer she delays the more the grandparents will think that they can win, and the less likely it is that they will EVER respect her decision. The third option, which we won't even consider, is actually going through with it. It won't turn out well, unless she its that lucky 1% chance. Which she won't.