Same problem here.
Me and my wife have killed her several times now, each time the PS4 crashes and puts us in XMB menu.
Tried different tactics: Massive AOE spells, Kill al summoned creatures first, kill Evelin first.
So we moved on with the rest of the quests, we've completed as much as we could and tried again but with no luck :(
(We've reported each error, PS4 error reporting)
