Wife of the Marshal de Belle Isle by Maurice Quentin de La Tour (location unknown to gogm)
Maurice Quentin de Latour completed a similar portrait of her husband around 1747 and this may have been a companion to that portrait.
From www.wikipaintings.org/en/maurice-quentin-de-la-tour/.
Fur may not be chic in the 21st century, but there a number of images in this Album (here, here, here, here, and here) suggesting fur was in style in the middle 18th century.
Keywords: de la Tour, Duchesse de Belle Isle, Duchess, French, long curly coiffure, off shoulder scoop neckline, bertha, lace, revers, fur, stomacher, close tight sleeves, forward-back flared engageantes, neck band, robes