Julia Montauk (Montork) Is the daughter of the serial killer Robert Montauk. She first appears is MAG 9: A Fathers Love where she has given her statement about her father's actions and motivations for the murders he committed when she was a girl.
Julia reappears several years later in MAG 107: Third Degree where it appears she met the Vampire Killer, Trevor Herbert, and the two of them began working as partners, traveling around and killing monsters until they ended up in the USA. In MAG 107, she and Trevor kidnap John during an encounter with (something???). She later gives a second statement in MAG 109: Nightfall which gives more details about how the pair first met and how they started working together.
In MAG 111: Family Business, it is revealed that the pair somehow obtained a copy of the Book of the Dead which contained the death, and therefore spirit, of Gerard Keay, who they have apparently been using as a sort of monster manual/dictionary to help them kill monsters. At the end of this statement, she and Trevor release John to return to England. Due to the illegal nature of their arrival in the USA, it appears the pair are stuck there.