Isabel is wearing a medallion of Nuestra Señora de Guadalupe in this and the last image (or an image that looks like the typical depiction of the Virgin of Gudalupe). This image is ubiquitous in northern California. This is not surprising - according to Wikipedia, "The basilica of Our Lady of Guadalupe is the most visited Catholic pilgrimage site in the world, and the world's third most-visited sacred site."
This is a copy of the preceding image on display at the studio Rubens worked in, preserved as a museum in Antwerp.
Keywords: Rubens, Infanta Isabel Clara Eugenia, Princess, Spanish, Habsburg family, straight coiffure, jeweled headdress, high enclosing neckline, lace neck ruff, surcote, tabbed sleeves, hanging sleeves, false sleeves, farthingale, necklace, earrings, jeweled crucifix, pendant, handkerchief, saya