Can't be a Primal. Blackbosom explodes into the usual purple mist (while Phoenix exploded the Primal way) and Edda disappears into a bright light (not at all like a Primal).

I think this is just a case of someone claiming the (lost) souls of the dead. Since Edda seemed to have some power over the Voidsent, whoever 'claimed' her probably thought it be best to make her the guardian of the Palace (50th floor was apparently overstaying our welcome).