The left side shows the portrait as available from an art reproduction seller, the right side shows the portrait as photographed where it is displayed, from here. I cannot find out who she was.
Please click on the image to properly view it.
Here is a Mignard portrait of a Lady in casual but formal dress. Marie Johanne's dress appears to have a high waistline - almost as high as in the Napoléonic era.
Keywords: Mignard, French, long curly coiffure, hair jewelry, off shoulder vee neckline, chemise, modesty piece, elbow length full sleeves, engageantes, split bodice, elbow length puffed sleeves, cuffs, waist band, Empire low waistline, full skirt, jeweled neckline, jeweled bodice, jeweled sleeves, wrap