She married Alfonso I d'Este, Duke of Ferrara, after the death of his first wife, Lucrezia Borgia. She had been Alfonso's mistress before Lucrezia's death in childbirth; Lucrezia was also unfaithful. Her terse Wikipedia article is here.
From www.everypainterpaintshimself.com/galleries/; spots throughout image, but especially in the background removed with Photoshop by gogm. The background was then blurred with Photoshop by gogm. The background is, therefore, heavily altered.