I was thinking, Elijah and Niklaus died because of Inadu's magic (maybe, because she did too) and, if by chance, they could kill her in the same way? I mean, a creature doesn't support a certain capacity for magic, even an immortal (as shown), right? And if Freya had put more magic on Inadu (like, a transfer spell) and left her "overwhelmed" to the point of dying for it. I know it sounds crazy and it would take, like, 5 originals to overload it, but it's worth it. Freya, Vincent, Niklaus, Rebekah, Kol and Elijah used their magic to transfer to Inadu and she would die as Finn died in the second season.