If I was her family, I would have burned this portrait. Based on this Wikipedia article about the Marquisate of Santiago, her name was apparently Soledad Rodríguez de los Ríos Sanche de Mastaing Álvarez-Bustamante Lasso de la Vega who lived between 1754 and 1807 married Antonio Bernaldo de Quirós y Mariño de Lobera, who lived between 1759 and 1798. She then married Joaquín de Magallón, Marqués de San Adrián.
From the Getty Museum Web site.
When Goya dumps on a subject, he dumps on a subject. The magnificent dress strongly contrasts with the plain and rather dumb-looking girl who is really about age 50.
Keywords: 1804, Goya, Soledad Rodríguez de los Ríos, Marquesa de Santiago, Rodriguex de los Rios family, Marquise, Spanish, straight coiffure, floral headdress, veil, lace, long close sleeves, cuffs, close skirt, maxi-length skirt, shoes, fan