The Naevus Heresy
Gallia was born on the corrupt planet of Bucephalon. She became involved in a death cult at a very early age, cleansing the corruption of the planet with the blade.
She was recruited into the Inquisition with a group of battle sisters fighting on the planet Hagia. Together they fought many minions of chaos and mostly survived.
More recently she has been working with Inquisitor Masters. She respects his tactics and trusts his instincts.