Every investigator can try to pet The Cat. Who does not appreciate a 3/3 soak, especially by the end of a tough campaign? But the XP cost is too high for just a soak and some, rather random, help on the road. If only you could mess with the chaos bag enough to take advantage of the upgraded modifiers The Cat brings?
Enter Jacqueline Fine. Even without Olive McBride and Charisma, even without Grotesque Statue she has much bigger chance to draw one of the tokens The Black Cat cares about.
A psychic should run a Sixth Sense, trying to fish symbol tokens (fish for a squid?) - but by the end of the campaign, these happen to be quite ugly and sometimes force you to make unpleasant decisions - The Cat fixes the problem! Even when Shrivelling someone, it's better to take a horror while passing a test rather than wasting a charge, failing a test, being punched back AND taking a horror.
Jacqueline's is something you like to ignore if you can, but if you need to use it, at least it can do something charitable - like healing The Cat!
Furthermore with The Cat by her side (on her shoulder?), Dark Future is much less of a problem, significantly decreasing the risk of Jacqueline's ending in fails with terrible consequences.