Her Wikipedia article is here. She was married to Lord Elgin, a British diplomat in Turkey, who took the Elgin marbles from the Acropolis of Athens to England with the permission of the Turkish authorities.
Countess Mary's dress is a glamorous version of French dress with gold embroidery, a lace fraise, a partlet on her décolletage, and jewelry.
Keywords: 1804, Gerard, Countess, British, curly coiffure, tiara, high enclosing neckline, fraise, lace, partlet, long high puffed sleeves, Empire waistline, close skirt, necklace, earrings