Infanta Isabella Clara Eugenia of Spain, (12 August 1566 – 1 December 1633) was, together with her husband Archduke Albert VII of Austria, joint sovereign of the Spanish Netherlands in the Low Countries and the north of modern France. In some sources, she is referred to as "Clara Isabella Eugenia".
She was the heir to the territories of the Spanish Netherlands and beloved of her nephew the Cardinal-Infante, Don Fernando, who was appointed governor-general of the Spanish Netherlands by his brother Phillip IV of Spain.
The arrival of Grantville somehow altered history in such a way to allow Infanta Isabella a longer lifespan. In the OTL, Isabella died in 1633. However, in the remade timeline, Isabella was still alive into 1634. A sharp confrontation with Gretchen Richter, who was not impressed with the Infanta's protestations of fragility, left many wondering if Isabella might live longer still, if for no other reason than to spite Richter.
For whatever reason, she did live longer, and served as a key advisor to her nephew, King Fernando.