The Malik shows her a variety of items, none of which are truly tempting except for a Robe of the Archmagi.
It's gray.
Neutral-aligned.
Carissa would have to Atone to Lawful Neutral to use it. But she keeps up a Mind Blank, so Hell wouldn't find out, right? "I wanted to be able to wear a gray Robe of the Archmagi" is something that any reasonable deity should understand as a just reason to Atone.