Why is she so retarded? She's a Duke's daughter! The fact that Prince, her fiance, keeps inviting her over specifically to watch him cheating with other women is basically a declaration of war against the Duke's family. He is directly saying that a Duke's daughter is worse than trash and she's his toy to play with and humiliate how he pleases. Why won't she tell the Duke what has been happening? That was the perfect moment! This is infuriating.
I'm seriously worried about all the people below who are raving about her attitude. All she did was antagonise her father, the Duke, while covering up the Prince's actions - effectively helping the Prince continue what he's doing. She just threw a tantrum and completely failed to even consider using her family and status, when her opponent is a Prince. Her best chance is obviously to leverage the fact she's a Duke's daughter. Why do you all think she was cool or a role model, or that this was somehow a victory?
Seems more like shooting herself in the foot.