Abigail's devotion to Diamond turned into a romantic relationship, and she was set on fulfilling the cult's plan to join the proverbial mother ship: which would require them to leave their "earthly vessels." However, while Abigail was out early one day, she spotted Diamond outside his car, and it was there that she realized that Diamond was a fraud. He coerced her to join him to spread their message--on a beach--while stating that he had a sedative that would knock out the other members. In a rage, Abigail killed Diamond with a blow to the head with a tire iron.
Diamond wasn't Abigail's only victim, as she later spotted Ty Bentley pleading with his ex-girlfriend (and one of the cult members) Emma Meyers to leave the cult, only for Emma to refuse. Ty vowed to take down the cult, and after hearing his threat, the evil Abigail killed Ty by shoving him down a flight of stairs. She and the rest of the cult covered up the murder, but later on, the deranged villainess set out on fulfilling the cult's original plan. Abigail made a cocktail consisting of Ketamine, a stronger drug than the sedative, and gave it to Emma and the other members, while planning to become the last to drink. She later watched the 11 other members die from her concoction, but after seeing them die, Abigail originally backed out of drinking herself and went home to her mother instead.
Later on, Abigail was spotted running to a nearby shed (after Jim Brass and the rest of LVPD arrived at her mother's home) and drank her concoction, but she was saved from her suicide attempt, as her stomach was pumped. While hospitalized, Abigail was interrogated by Gil Grissom, and she voiced her envy of her 11 former members, as she stated that they were in a higher plane of existence. She expressed no emotion regarding the mass murder, and it was revealed that she didn't tell the group about Diamond or that she killed him. As for Ty, Abigail only referred to his death as "unfortunate," and it can be assumed that she was arrested (off-screen) for her immense amount of murders.