She was an Eirikrson.
They were monsters. Vampires who only drank vampire blood. The head of their family had created the huntsmen to hunt down and murder any vampire—not just the rogues, at the beginning. When she turned, she'd be just like them, the nightmare they whispered about in the dark.
The reasonable thing would be to destroy her before she could obliterate hundreds of years of peace. She wasn't a little boy Levi couldn't bring himself to murder. He should have beheaded her in London. He should have ordered Mikar to burn her alive, if he was too squeamish to do it himself. But he couldn't, because fate was a bitch. Like it or not, he was on the girl's side.