Elise might not have seemed like the go-to person to close inter-dimensional portals, and she definitely felt that way herself, but really she was the ideal candidate considering the way these reality tears worked.
Elise studied under the teachings of Sylvi who, amongst being the Goddess of Trickery and having many other names and feats, was responsible for separating the worlds through her Divine Mist. At least that was what it was in Dawd's Lore, which at this point could simply be considered real life history which was definitely not disturbing to think about.
Somehow, the Trickery Goddess had separated realities, such as the realms of the living and those of the dead, through veils of mist. The mist constructed illusions so perfect and believable, that it tricked reality itself into thinking that they were actually separate and thus the realms did not interact or perceive each other.
