Seraphina Lumanis, of the Sanctum of Mercy
Importance:
One of the seven called to the Sentinel trials. She is the one who tells Via that something already has a claim on Xanthe's soul - a bargain with a devil, she believes - and Via pleads until Xanthe agrees to be examined. Seraphina wins her trial. Then the heirs are escorted out of the tournament grounds into a line of cultists, and she is standing in it, with Brenna Stonehill and a dragon beside her. The party escapes the fight. So does she.
Since then
I told your sister nothing about herself that was untrue. That is what makes it work.