She was played by Natassia Malthe, who previously appeared at Typhoid in the action film, Elektra.
Sonja is the lone female member of a group of evil werewolves, led by Varek, who was once known as Caleb and married to protagonist Rachel. She was once human and lived a terrible life, but she became a werewolf when Varek turned her. Sonja since became Varek's lover, and has shown devotion to him and the group's cause, which is to maintain their lives as werewolves and take over. Part of their mission included planning to kill young Timothy, who is Rachel and Caleb's son, and when Sonja learns the truth about Timothy, she takes the mission personally due to her hatred of Rachel. In the film's climax, the evil Sonja hunted for Timothy and Rachel with intent on killing both of them, only to end up shot by Timothy. Sonja was weakened by the shot, but it was Rachel's own shot that would kill Sonja.