Her Wikipedia article is here.
From gixcel.com.
Marchioness Frances Anne wears a typical early post-Napoléonic evening dress from curly coiffure, to the square neckline and short puffed sleeves, to the high waistline, to the close skirt in this 1818 portrait.
Keywords: 1818, Lawrence, Francis Anne Vane Tempest, Vane family, Tempest family, Marquise, British, curly coiffure, square neckline, modesty piece, quarter length puffed sleeves, waist band, Empire waistline, close skirt, necklace, brooch, bracelets