Margaret became a queen dowager and the regent of Naples as the guardian of her minor son from 1386 until 1393. In 1387 she poisoned her elder sister Joanna, Duchess of Durazzo, who might have a better claim to the throne of Naples, and her husband Robert IV of Artois, Count of Eu to death. She survived her husband by twenty-six years but never remarried. Their son Ladislaus succeeded to the throne of the Kingdom of Naples while Mary of Hungary was restored to her throne. Margaret insisted that her husband's death be revenged and Elizabeth was murdered. The heads of her defenders were sent to console Margaret.