"Obsessed with his wife"... Crown Prince, you clearly don't understand other normal human beings. Rowan loves his wife. And unless people are stupid and wish to tear down Erin from her high seat as the Duchess (which even if she died, no one else can take), who would believe that she killed Claire? I'm pretty sure the Palladines were banished and any rational person would know that Erin would not find Claire a threat. She's also a prisoner of war as the prince said himself so why would she bother to act up and kill someone who was banished? Also, she was banished. Said this three times but how would Erin know where the fuck Claire was to kill her? There should be enough people in the Port of Duan to see how frantic the Duke was trying to find his kidnapped wife... so stories would spread about that already before the prince could make his move. If anything, it would have been Erin's self-defense move from Claire having motives to kill her. This is such a weak plot point if this works out. There's too many things that would go against it working out. Rowan would also have enough vassals under him to take care of this too. He's both rich and powerful after all. Royalty only has so much power if they don't have loyal vassals as well.