A Maricopa County jury, which previously found her guilty of murdering 10-year-old Ame Deal, had decided to sentence her to death.
Allen is accused of locking Deal, her younger cousin, in a storage locker overnight after she took a Popsicle from the freezer without permission.
During the trial, jurors heard testimony about the other abuse that Deal had endured during her short life, including being forced to eat dog feces and walk barefoot on the sidewalk in 114-degree heat. At least one juror had to be excused, telling the court that the emotional toll of the case had made him unable to render fair judgment.
Allen's defense attorney argued that harsh punishment had been normal in the household that she grew up in, and that she took her cue from her own mother and Deal's legal guardian, Cynthia Stoltzmann.
As a result of her own troubled upbringing, Allen dealt with depression, attention deficit disorder, exposure to parental child neglect, and impairments in brain and moral development, and had lower than average intelligence, according to a psychiatrist for the defense.
However, jurors only heard a limited amount of information about Allen's mental health during the trial.
The verdict will make Allen the third woman on Arizona's death row. No women have been executed in the state since the botched hanging of Eva Dugan in 1930.
The trial for Allen's husband, John Allen, is currently underway. He is also facing charges of murder and child abuse.