Fernando and Isabel married in 1469, but this portrait could have been completed later.
From Wikimedia.
Isabel's dress is little different from that worn by Isabel of Portugal for her 1548 Titian portrait except for the caul, veil, and pendant combination. If this is an accurate depiction of her dress, then elements of farthingale style were in place in the third quarter of the 1400s.
Keywords: Isabel I, Isabel la Católica, Isabel de Castilla, Queen Isabella, Trastámara family, Princess, Queen, straight coiffure, caul, veil, pendant, vee neckline, partlet, square neckline, bodice, necklace, brooch