She would spend the rest of her life in her estate in Löbichgau, where she would invite and host many important political and cultural figures of the time and make many acquaintances, ranging from Goethe over Napoleon I of France to Talleyrand, the latter of whom she was reportedly very close.

Her father, a descendant of Konrad von Mandern, was himself awarded the Order of St. Alexander Nevsky in 1774 for his help in preparing the Treaty of Küçük Kaynarca.

Because her husband was preoccupied with political difficulties at home involving his overlord the King of Poland and the Courland nobility, he frequently sent her on diplomatic missions to Warsaw, lasting months at a time, and to Berlin, Karlovy Vary, and Saint Petersburg for shorter periods.

During these long absences Dorothea became alienated from her husband and had numerous love affairs with other men, including Gustaf Mauritz Armfelt, Talleyrand, and the Polish nobleman, Count Alexander Benedykt Batowski, who allegedly fathered her fourth daughter, born in 1793.

After the year she gave birth to her daughter, also named Dorothea (whom her husband nevertheless acknowledged as his own), the Duchess moved permanently to the Palais Kurland in Berlin, where she held an aristocratic salon.