Dr. Theodora "Teddy" Lowe is a new anesthesiologist hired by Sean and Christian at their new L.A. practice. Romantically involved with Sean, she soon convinces him to marry her in the season 6 premiere. However, Sean has no idea that Teddy is in fact a "Black Widow," (a female serial killer who marries men and later kills them) and is living a double life. As revealed in the Season 5 finale, Teddy was going by the alias "Dixie" in a small Las Vegas plastic surgery firm. She married the owner, Harlan, but soon killed him... presumably for his money. Teddy then focused on Sean and proving to stop at nothing to get at his health insurance money, going as far as to murder a patient who recognizes her while Teddy was working in Vegas under her "Dixie" alias.

During a camping trip with Sean, Annie and Connor, Teddy tries to kill all three of them by drugging them with sleeping pills and flooding the camper with carbon monoxide. However, Annie wakes up (having not eaten the drugged smores) and manages to wake her father up who manages to break the door down and get them out. Teddy walked off and encountered a nearby camper who turned out to be another serial killer (a man who kills women). Teddy was attacked by him and runs back to Sean to find the trailer empty and her attacker behind her. Sean is later called by the police, who find a human heart in the forest nearby who's DNA matches blood from Teddy's hair. The attacker is later pulled over for a routine traffic violation and is arrested when he is found with bloodied hands... and Teddy's severed head in his car trunk. Sean later learns that Teddy intentionally tried to kill him and his children, and had preyed on and murdered at least four other doctors in the past as well. Before attempting to commit suicide, Sean dumps Teddy's ashes into a trash can and throws his wedding ring in after it. (deceased)