I think you have dreaded telling the parents for so long it almost has you in panick mode. Maybe you should not worry what you'll say. She needs to tell them in front of you. If she makes it sound as if it's what both of you want, or that both of you have agreed, then you need to tell them it isn't what you want, etc. I don't think you should leave with them thinking you are supporting the idea of D.
Stop worrying about what kind of emotion to show or not show. Be yourself and be truthful. It is a sad occasion.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!
