User blog comment:ND999/Lore Hypothesis, Mt. Targon, Guardian Sea and Shadow Isles/@comment-7709681-20141115150533

Unlikely that she's from Mt. Targon, and if she is Riot isn't giving it relevance, for what was hinted on Kalista's Q&A, they are focusing on that she was likely a member of the Ruined King's royal guard (Or at least a warrior very close to the Ruined King), and she died the day that the isle became what currently is.

But oh Lord-y, I absolutely love the Nautilus link with Kalista/The Black Mist, I don't know how that has got so far unnoticed.