Briana is a descendant of a long line of white witches who for centuries have generally lived their unnaturally long lives while doing their best to protect their families, tribes, communities, villages, and towns from the depredations of evil or ill fortune. Often even in the face of superstitious persecution.
However Briana's mother was killed while trying to root out a den of vampires in London over four decades ago, and afterwards Briana sought a new life in the new world to put some time and distance between herself and her mother's death. Her tourist visa eventually ran out but Briana remained in the States, wandering from city to city. For the most part she lives a carefree life of whimsy, but from time to time she encounters various supernatural dangers. If possible she informs local Hunters, assists their Hunt as best she can without getting directly involved, and collects a finders fee from any resulting bounty; otherwise she notifies Section M and lets them deal with it.
Section M are aware of her illegal immigration status but have chosen to look the other way thus far; perhaps because while Briana may not be a front-line fighter in the war against supernatural evil, her intel has always been good.