Christina was the child of Selena Curiana and Belor de Velland. When he died Belor used some sort of Black Flame ritual to accelerate her aging process and turn her in to some sort of entity of the Black Flame. In addition to a strong association with the Flame, she also inherited ties to glass and ash from her mother (her blood is both ashen and shattered). She believes that the White City wronged her parents and is determined to get revenge. Perhaps more redeemingly, though, she also is a strong supporter of the rights of the ordinary people to be able to realise their potential. Perhaps she might be able to be brought over to a better path, perhaps not, only time will tell.
Christina has one half-sibling by the name of Toquell Curiana (the son of Selena and Paulo). He resides with his grandmother Maria Curiana and has some sort of spiritual connection to Christina. More can be found here.