Wanda Jean Allen was born on August 17, 1959, as the second of eight children in the United States. She grew up in a challenging environment. Her mother struggled with alcoholism, and her father left the family when her youngest sibling was born. As a result, they lived in public housing and relied on public assistance to get by.

When Wanda was 12 years old, a serious incident occurred. She was hit by a truck and knocked unconscious. This was not the only traumatic event in her early life. Around the age of 14 or 15, she was stabbed in the left side of her head. These incidents impacted her health. Medical evaluations revealed that Wanda had an IQ of 69, which is considered low. It was discovered that there was dysfunction in the left hemisphere of her brain. This affected her ability to understand and express herself logically and made it hard for her to analyze cause and effect. Research indicated that she was more sensitive to stress than most people. By the time she turned 17, Wanda had dropped out of high school. 

In 1981, Wanda Jean Allen shot and killed her girlfriend Dedra Pettus during an argument in their apartment. Allen claimed that the shooting was accidental and occurred while returning fire from Pettus' boyfriend. However, forensic evidence suggested otherwise. The police found bruises and powder burns on Pettus' body indicating that Allen might have pistol-whipped her before shooting her at close range. Despite this evidence, Allen pleaded guilty to manslaughter and received a four-year sentence, serving two years.

Seven years later, Allen was in a relationship with Gloria Jean Leathers. On December 2, 1988, Leathers was shot in front of the police department. Prior to the shooting, the couple had a dispute at a grocery store, after which Leathers was escorted by an officer to retrieve her belongings. When Leathers went to her car, she hit Allen in the face with a garden rake. Allen later followed Leathers and, after returning to her car for a gun, shot Leathers as she approached. Leathers died from her injuries three days later.

In the trial for Leathers' murder, the state charged Allen with first-degree murder and sought the death penalty. While Allen's defense argued self-defense due to Leathers' violent history, the prosecution depicted Allen as a liar. The jury found Allen guilty and sentenced her to death. During the sentencing phase, the prosecution presented details of Allen's previous conviction and portrayed her as a continued threat to society.

Allen spent twelve years on death row. Her clemency application was denied despite arguments about her mental capacity and educational background. On January 11, 2001, Allen was executed by lethal injection in Oklahoma. During the execution, she uttered a statement of forgiveness. Allen was pronounced dead at 9:21 p.m., and her execution was witnessed by relatives of both victims. She was buried at Trice Hill Cemetery in Oklahoma City.