Yeah, I was also thinking about the King/Emperor thing. Cardinal/Church people would also be a nice choice, I hadn't thought of that and if it all fails, she can just go ballistic and say, "Your Majesty, I will never marry the Crown Prince. I would rather die than marry someone who thinks it's appropriate to show his fiance how he seduces and sleeps with another woman. A man who sleeps with a different woman every day. I would rather wish you for you to kill me, than to force me to marry him." Then something about killing the duke's daughter bringing political instability (angry duke) + probably angry subjects + a bad precedence.