I’m curious if anybody has considered it might be in the Temple of Lyssa. I recently completed my personal story quest, and during the quest leg in Temple of Lyssa, Trahearne specifically said the temple was the final resting place of her followers or something like that. I forget the specifics of the dialog beyond that, but “final resting place” is word for word. I perked up as soon as I heard it. Apologies if this doesn’t contribute to the search, but I thought I’d mention it just in case!