Her Wikipedia article suggests the portrait could be located at Statens porträttsamling, the Swedish National Portrait Gallery, in Gripshoms slott, Mariefred, Södermanland, Sweden. She was the daughter of a Swedish official given a noble title. She was a poet, feminist, and salonist.
From Wikimedia; enlarged one quarter. Also posted to the Reign of Louis XV - 1715 to 1774 Album here.
She died in 1763. The coiffure suggests the portrait was painted in the 1760s.
Keywords: Pasch - Ulrika, Hedvig Charlotta Nordenflycht, Swedish, curly coiffure, headdress, choler neckband, bows, neckband, bodice, square neckline, lace collar, lace modesty piece, stomacher, bows en échelle, three quarter length close sleeves, lace engageantes,