Guadalupe was the mother of several boys. They moved to New York City from Mexico, presumably Zacatecas.
In 1953, rumors of a vampire taking victims from their neighborhood spread. As it turned out to be true, a gang of young boys banded together to protect their neighbors and hunt down the vampire. Guadalupe's eldest son, Raphael, at fifteen years old, joined. More worried for the safety of her younger sons, she did not take the gang's antics too seriously.
One evening, however, Raphael did not return home after a raid the boys planned on the vampire's lair, the Hotel Dumort. A few days after, Guadalupe became desperate with worry that she finally approached the warlock Magnus Bane, someone known by those who know enough of the Shadow World as someone who helped people for a price. She became Magnus' first client as a "detective".
Guadalupe's words while asking Magnus to save Raphael stayed with him, even after he found Raphael Turned into a vampire himself, beyond saving. For her, both Magnus and Raphael strove to have him achieve a semblance of humanity, such as being able to touch and wear his cross, stepping over holy land, saying "Dios", and controlling his hunger for blood.
Guadalupe kept in contact with Magnus since they first met, with Magnus insisting that Raphael was fine. After months of his absence, Raphael finally came home one evening. Magnus claimed that Raphael was dying when he found him and needed to make Raphael like him, an immortal warlock, knowing that Guadalupe did not fear him the way she did vampires, and that they had been training with Magnus during his absence so he would be fine enough to go home to them. Initially skeptical, Guadalupe welcomed Raphael back into their home and family.
Guadalupe later thanked Magnus and intended to pay him. Magnus refused her payment, however, and told her that she knew as well as he did that Raphael saved himself, that she had raised him well and should do the same with the rest of her children.
Guadalupe was a small, charming woman who looked to be in her late thirties. She had a small waist, black curling hair, a small heart-shaped face, and thin eyebrows that gave her a challenging air that was both attractive and intimidating.