Duke Rannucio I died on 5 March 1622. His younger brother, Cardinal Odoardo, acted as Regent of the Duchy of Parma on behalf of his 10-years-old nephew and new Duke Odoardo. The Cardinal's death in February 1626 allowed Margherita, now Dowager Duchess, to become in the new Regent for her son. Her 2-years regency transcurred during the Thirty Years' War; she managed to maintain stability in the Duchy, observing neutrality. In the War of the Mantuan Succession she supported Charles Gonzaga, Duke of Nevers, who became in the next Duke of Mantua and Montferrato.