The US Supreme Court has refused to halt the Virginia execution of Teresa Lewis, scheduled for Thursday.
She is the first woman to face the death penalty in the US for five years.
Teresa Lewis, who has learning difficulties, conspired with two men to kill her husband and stepson in 2002, leaving a door unlocked so the gunmen could enter the family home.
Two of three women in the nine-judge court voted to halt the execution.
Justices Ruth Bader Ginsburg and Sonia Sotomayor voted against. but there was no other comment from the court.
Virginia Governor Robert McDonnell has said he will not commute the death penalty, despite claims Lewis, who pleaded guilty, has learning disabilities.
The two gunmen who carried out the killings received life sentences.
Lewis - due to die by lethal injection on Thursday - will be the first woman executed in Virginia since 1912.
Her lawyers filed a petition for executive clemency on 25 August 2010.
Declining to commute the sentence, Virginia Governor Robert McDonnell said: "Lewis does not deny that she committed these heinous crimes.
"Numerous psychiatrists and psychologists have analysed Lewis, both before and after her sentencing.
"After numerous evaluations, no medical professional has concluded that Teresa Lewis meets the medical or statutory definition of mentally retarded".
Lewis's husband, Julian Lewis, and stepson, Charles Lewis, were killed with shotgun blasts by Matthew Shallenberger and Rodney Fuller at their home in Danville, Virginia.
BBC News
