"Constance isn't just a cat. She is my sister...Well, she was. I mean, she is, but she's not like she used to be. See, she's under a curse, cast by the mystic Tia Dalma herself." "Was the spell cast because she was this vile in her previous incarnation?"
Constance and Jean became sailors at a young age, but an encounter with Tia Dalma left Constance in the form of a cat. Jean continued to treat Constance as his sister, and was highly protective of her. The two met and befriended Tumen, and, around the age of twelve, they worked together aboard the Seraph. It was while unloading the ship's cargo at the docks of Martinique that the trio encountered Left-Foot Louis. Constance accidentally tripped her brother while Jean was carrying a crate of silk, causing him to fall at Louis' feet. Constance leapt at Louis before the pirate could punish Jean, and tore her claws across Louis' face, marking him for life. The trio were able to escape after Louis was set upon by the crew, though not before he swore to skin Constance alive upon their next meeting.
The Magliores and Tumen sailed together for almost a year following their escape from Louis, and were aboard the Seraph when it was caught in a storm conjured by Captain Torrents. The trio were the only survivors, washed up on the shore of Isla Esquelética, where they were forced to eke out an existence, and began constructing a raft to return to their home port.
It was on Isla Esquelética that the three met Jack Sparrow, Arabella Smith and Fitzwilliam P. Dalton III. Sparrow's crew was initially wary of Constance, and were dubious over Jean's claim that Constance was really his sister. Nevertheless, Jack allowed the Magliores and Tumen to join his crew, and together explored the City of the Dead, and survived a confrontation with Torrents.
Shortly before Jack Sparrow's quest for the Shadow Gold, Constance was turned into a human again. When the Black Pearl docked in New Orleans, she joined the ship's crew, but she started to introduce herself as Jean's cousin, Marcella, to hide her previous participation in Jack's adventures. Later, she fell in love with Diego de Leon, although he was not attracted to her in any sense and was instead infatuated with Carolina, a rogue Spanish princess. Constance would compete fiercely for Diego's affections, even resorting to telling the Spanish, who were tracking Carolina, where she was. After the Day of the Shadow was over, Jack found out that she and Constance were, in fact, the same person.