It was explained on the Website.
In the aftermath of Ubersreik, Kerillian’s dreams were a jumbled cacophony, and one of the most lucid visions spoke of an ancestor who bore the exiled blood of Clar Karond. The dreams did not emphasise the future, but here and now. Through the mists of memory, a cruel voice spoke, urging her to reclaim the mantle of her forebear. Her count continues, but in glory, not in penance.
As a Shade, Kerillian treads an assassin’s path, striking unaware or distracted foes when they are most vulnerable to her wicked blades. She is fleet-footed death, come to claim the blood of the living.