She was the daughter of Infanta Catalina. Her Wikipedia article is here. She bore 14 children and died bearing the fourteenth who survived her mother.
From the-athenaeum.org. Also posted to the Iberian Style in the Farthingale Era Album.
Isabella is shown wearing a fur neck band and a conical cap. This image and this one show the link between Italian and Spanish styles.
Keywords: Anguisola, Isabella di Savoia, Savoia family, Este family, Duchess, Italian, wavy coiffure, jeweled feathered headdress, fitted bodice, high neckline, lace-edged deep neck ruff, jeweled fur neck band, jeweled fur neck band, jeweled bodice ornament, tabbed hanging sleeves, lining, long false sleeves, ruffled cuffs, waist band, vee waistline