From Wikimedia.
The saya has been superseded by the tontillo style in this portrait. Her dress has long puffed sleeves with single slashes along the lengths of the arms and the characteristic high straight neckline.
Keyword: de Tovar, Marquise, Spanish, long straight coiffure, hair ornament, off shoulder straight neckline, bertha, lace, long puffed sleeves, slashed sleeves, back flared engageantes, vee waistline, full skirt, fan