This is a lower quality portrait of Catherine de Medici wearin a black and white dress.
The Wikipedia article for Santi di Tito is here.
The rolled portions of her sleeves are slashed. She wears a necklace attached to the sides of her neckline and another connected to a brooch on her bodice using graceful swags on each side of the brooch, something ladies wore up to World War I.
Keywords: di Santi, Catherine de Medici, Medici family, Valois family, Queen, French, draped necklace, shallow necklace, jeweled neckline, French hood, jeweled headdress, bracelets, jeweled bodice ornament, French sleeves, girdle, jeweled pendant chain