From Wikimedia; image made lighter by gogm.
The Marquise wears an Empire dress with what appears to be a train that falls from her waist band and, possibly, a bodice panel covering her back to distribute the load between waist and shoulders. This portrait also provides an excellent view of how her shoes touched the floor.
Keywords: 1804, Goya, Maria Gabriela Polafox y Portocarrero, Polafox y Portocarrero family, Portocarrero y Portocarrero family, Marquise, Spanish, curly coiffure, ribbon headdress, square neckline, quarter length close sleeves, waist band, Empire waistline, close skirt, train, shoes