Her genealogical sketch is here. According to her Wikipedia article, she was a fine pianist and a patron of Mozart and Beethoven.
From the museum's Web site; increased contrast and enlarged by half.
Marie Wilhelmine’s coiffure is pre-Revolutionary bouffant style, but her dress shows strong classical Revolutionary influence.
Keywords: 1790, Füger, Maria Wilhelmine von Thun und Hohenstein, Uhlfeldt family, Thun und Hohenstein family, Countess, German, bouffant coiffure, jeweled ribbon headdress, veil, bodice, scoop décolletage, elbow length close notched sleeves, jeweled arm bands, close skirt, over-dress, assymetric neckline, strap sleeves, clasps, waist band