Whoever wrote this quest is a heartless bastard.
The undead cat has been standing watch over the possessed girl, it's master, for who knows long.
You can take the girl with you to the Lady Vengeance, but not the loyal cat? Why not? There is no logical reason to separate them.
You even went through the trouble of changing and voicing the cat's dialogue after the girl is gone. Oh, and you leave it alone down in a pit... Really? YOU MONSTER.
From what I've read elsewhere the quest is a dead end and doesn't advance after you bring her back to the ship. People who have completed the game said it was never addressed again.
