Her Wikipedia article is here. An image of her sister Elisabeth is here.
From Wikimedia.
Catherine wears a dark sleeveless surcote and a gold brocade dress below it. Her sleeves are decorated with numerous puffed cloth ornaments.
Keywords: 1557, Monogrammist PF, Queen Catherine of Poland, Habsburg family, Jagiellonowie family, Archduchess, Queen, jeweled cap, escoffion, partlet, high enclosing neckline, ruff, carcanet necklace, necklace, fitted bodice, square neckline, French sleeves, puffed cloth ornaments, contrasting flared cuffs, surcote, strap sleeves, full skirt