This is an early work of the great Spanish portraitist Vicente López y Portaña whose Wikipedia article is here. He is not well-known in the USA, but should be.
The Duchess wears a jumble of a huge hat, big coiffure, fichu, and wide skirt speared by her vee waistline in this 1795 López y Portaña portrait.
Keywords: 1795, López y Portaña, Duchess, Spanish, curly coiffure, feathered hat, fichu, lace, elbow length tight sleeves, engageantes, vee waistline, panniers, over-skirt, flounces, earrings, fan