Isabella is wearing something that looks like an embroidered chemise or under-garment. She also wears a large carcanet necklace.
Keywords: 1606, Pourbus - Frans the Younger, Isabella di Savoia, Savoia family, Este family, Duchess, Italian, wavy coiffure, tiara, hair ornament, earrings, necklace, under-bodice, high vee neckline, tabbed basque bodice, lace-edged neckline ruff, collar, carcanet necklace, jeweled pendant, tabbed hanging sleeves, clasps, lining, long false sleeves, lace back-flared cuffs, full skirt, saya