Emma Spool was the sister of Norma Spool, and was equally (if not more) mentally unstable as her sister was. Emma was in love with Norman's father but he chose her sister and after her nephew, Norman was born, Emma went mad. She believed Norman was the child she should have had with Mr. Bates, which caused her to fly into a rage, murder Mr. Bates and briefly kidnap Norman (Psycho III). Spool was institutionalized for many years for this act. She was not released until after Norman was arrested for the murders of Marion Crane and Milton Arbogast. Upon her release, Spool got a job working at Statler's Diner and later convinced Ralph Statler to hire Norman as well.
Still mentally ill, Spool believed Norman was her son. After Warren Toomey drunkenly confronted Norman at Statler's, she murdered him and dumped the body in the swamp on the Bates property. When she discovered that Lila and Mary Loomis were trying to drive Norman mad, she murdered Lila. Spool also murdered a young man named Josh when he and his girlfriend snuck into the Bates House and saw her.
After Norman had been cleared of any wrongdoing, Spool visited him and told him that she was his "real" mother. Norman served her poisoned tea as they spoke and hit her over the head with a shovel, killing her. He then kept her body as he had years earlier with Norma Bates (Psycho II).
Tracy Venable, came to the bates house and motel to find the missing Emma Spool. She told Norman Bates, (who continued the whole mother persona with Emma's corpse) that Emma was really his aunt, she lied to him that she was his real mother and she killed his father Mr. Bates out of jealousy in a love triangle between them and Norma Bates, then Emma kidnapped Norman claiming he was her and Mr. Bates' love child. Enraged by the deceit, Norman snapped out of his delirium and destroyed Emma's corpse but he was once again sent to the asylum, though Norman was glad he was free from her.