According to Catherine's account, it was somewhat tragic. Her family had kindly rescued an elderly man, but after he woke up, he sacrificed her entire family, leaving only her behind.
Lance could roughly guess that it was because the Wizard noticed her Extraordinary Talent that he spared her; otherwise, the Wizard certainly wouldn't have left her alive.
Then Catherine was taken by the Wizard's side, forced to become his apprentice, or rather, a servant, a mobile blood pack.
At the time, the Wizard seemed to be pursued by some enemy, and that's why he left Levant with a merchant ship to seek refuge in Totnes.
Additionally, he disguised his identity under the guise of an antiques dealer. This ancient being, who knows how long he has lived, actually did know his stuff, quickly setting up shop on Rat Street.
During this time, to ease his own burden, the Wizard did teach her a lot, and he also involved her in some of his rituals.
