Only with the predictable demise of the Imperial Reichspost , the German Mediatisations of 1803 , the mediatization of the Princely House of Thurn and Taxis , and the loss of position of Post Master General in the time of Napoleon I of France , Therese became outwardly politically active , most especially after the death of her father-in-law in 1805 . Since then , Therese reinforced the sovereignty of the Princely House of Thurn and Taxis and its traditional postal rights . In 1806 , she and her husband negotiated with her brother-in-law Frederick William III of Prussia along with Karl Theodor Anton Maria von Dalberg , the former Archbishop-Elector of Mainz and Prince-Primate of Regensburg , and for the first time in 1807 with Napoleon . Likewise , they also negotiated with Maximilian I Joseph of Bavaria in Munich and proposed to him the nationalization of the Thurn and Taxis Lehnspost there . In 1808 , Therese and her husband took the interests of the Princely House of Thurn and Taxis to the Congress of Erfurt . There , a secret meeting occurred between Charles Maurice de Talleyrand-Périgord and Alexander I of Russia in her salon
Congress of Erfurt
Congress of Erfurt
Duchess Therese of Mecklenburg-Strelitz