The final insult was when he jumped off her back to stomp her wand into two useless pieces. Even if she was somehow able to untie her wrists, she had nothing to fight with. It was only then that she got a good look at Rodolphus" second accomplice. She just had to laugh or she feared she would go mad with worry. How persuasive did Rodolphus have to be to get such a distinguished and respected member of the Resistance on his side?