Her genealogical sketch is here. According to her husband’s Polish-language Wikipedia article, he was unscrupulous. But she was mistress to King Augustus II of Saxony. The museum’s English-language notes include this, “...The painting seems to fittingly show the sitter’s character—her dynamic pose and masculine costume are very telling about her personality. Widowed early in 1730, in September Emercjanna was already remarried, to Joseph Alexandre, Count de Montmorency de Bours (d. 1759)…”
From Wikimedia; partially fillled in shadows. Also posted to the Reign of Louis XV - 1715 to 1774 Album.
Long powdered wigs were commonly worn by men and she appears to be wearing one in this cheesecake portrait. The jacket sleeves have large cuffs.
Keywords: Mányoki, Emerencjanna Warszycka, Emerencjanna Pociej, Warszycki family, Pociej family, mistress, Augustus II of Saxony, long curly coiffure, fur-trimmed tricorne hat, neck bow, jabot, jacket, long close sleeves, contrasting cuffs, buttons, chemise, U-décolletage, fitted bodice, vest