The Great Mother was a powerful Rank 9 Archdemon that was supposed to have fallen during the Cataclysmic War at the hand of an ancient powerhouse of the Immortal Plane. Usually, the only fate of those that lost their foothold in Abyss was to have their True Soul devoured by the plane's origin. That is why no one believed she could still be alive.
However, Zatiel was confident things were not so simple. His knowledge about Abyss was vast. While he had been the only Archdemon that did not evolve into Rank 7 by fusing his True Soul into the plane's origin, there was no reason others couldn't retrieve it if they were powerful enough.
The Neo-Demon believed that the Great Mother had endured severe injuries after that battle and knew other Archdemons would take advantage of her situation. Using some arcane methods, she retrieved her soul from the plane's origin and came into hiding.
