In 1789, she became a widow and possibly entered into a secret, morganatic marriage with the King, remaining known at court as his maîtresse-en-titre. However, Wirydianna Fiszerowa, a contemporary who knew her, reported that tales of this marriage only circulated after Poniatowski's death, and were spread about by Elżbieta herself, but were not generally believed. She was thought to have exercised some influence on the king during his reign perceived as negative, which made her unpopular.
In 1795, King Stanisław abdicated following the Third Partition of Poland, and lived in Grodno under Russian watch until, in 1796, Paul I of Russia invited him to Saint Petersburg. Elżbieta, with her two sons, Stanisław and Michał, took the king to Saint Petersburg to care for him there, and she lived with him until his sudden death in 1798. Afterwards, she returned to Warsaw, then under Prussian rule following the Partitions, where she became a patroness of the Tableau vivant there. She died in Warsaw on 1 June 1810, survived by four of her children.