Constance Mayer was hosekeeper, nanny, student, and mistress of Pierre-Paul Prud'hon. Many works attributed to him may be hers. A biographic article can be found here.
Sophie Landon wears a dress with a rounded vee (Basque) waistline that is unusual for the era in this 1820 Mayer portrait. Her partlet covers what could be a revealing neckline.
Keywords: 1820, Mayer, French, straight coiffure, floral headdress, bateau neckline, partlet, quarter length puffed sleeves, basque waistline, close skirt