In 1761, she became an ally of Stanisław August Poniatowski, and gave him a loan of 300.000 zloty, with a great interest, to fund his political career: he was still paying of the debt six years later.

Her influence on Poniatowski, both in her capacity as his lover and his moneylender, was well known, and the king included her in his inner circle of advisers and entrusted her with political assignments.

In a letter from 1768, the king described her as irreplaceable among his "petites amies" (lovers) and called her wonderful, warm, intelligent and an extremely useful ally.

Her gender was no formal bar for this activity; within the contemporary Polish system of an aristocratic elective monarchy, her membership within the nobility was the main criteria.

In 1774, her brother, Franciszek Ksawery Branicki, joined the opposition against both the king and the Russian ambassador Stackelberg, with whom Branicka had a bad relationship.

Elżbieta Branicka was a controversial figure in contemporary Poland, and her activity as a politician, particularly during the Great Sejm, made her the subject of satires, pamphlets and poems by, among others, Ignacy Potocki and Franciszek Zabłocki.