That is none of your business, so I'll thank you not to ask.
History With Frank DoyleEdit
Catherine was Frank's first love (just as he was hers). She came to the church running from her own demons, much like Frank did.
She was killed while the two of them were investigating a series of Calaca attacks. Father Lancaster sent her off on her own, and she was caught by the Calaca and danced to death. Frank later killed the Calaca responsible, and waited a full year to bring her back from the dead. However, as Frank had killed the Calaca, Catherine was trapped by him in the afterlife.
Years later, Catherine manages to escape the Calaca by hiding his marigolds. She visits Frank and Sadie, who defeat the Calaca and help Catherine escape for good.