Matsushima's sense of morality is something else. She pulls out all the stops to avenge a wrong. If Sano hadn't gotten in trouble while getting a gift for Ichio, Matsushima would've likely just left it alone. It makes me wonder if she would've also let things be if Sano was Ichio's only 'wife' and had gotten in trouble for theft, or if it's just Sano getting into trouble at all for the sake of someone else that pushed Matsushima's buttons.