Since they have Berenike, one of the enraged undead from the Necropolis, and are gonna be trying to figure out what's wrong with her:

What would Kostos (who can read spirit minds etc.) be able to pick up from her, either in terms of memories of The Event or the current state of the spirit possessing her?

Would putting a new wisp into the corpse cause the new wisp to go bad as well? Similar vein, would removing the wisp from her entirely/binding it into something else cause the original wisp to chill out? (Basically looking for whether the problem is with the corpse or with the spirit, if not both.)