A genealogical sketch of her is here.
It took a while for the Greco-Roman look to sweep all of Europe as can be sen by the fullness of Countess Maria Theresa Czernin's skirt. Fashion appears to have slowed to a glacial pace - the Countess' dress could be from 1788.
Keywords: 1793, Vigée-Lebrun, Maria Theresa Czernin, Schönborn-Heussenstamm family, Czernin family, Countess, Austrian, long curly bouffant coiffure, feathered ribboned hat, scoop neckline, modesty piece, wrap, long tight sleeves, full skirt