“She is clearly the head of this serpent,” the judge said of Teresa Lewis in 2003 when he sentenced her to death by lethal injection, describing her as the mastermind of the cold-blooded murders of her husband and his son as they slept in rural Virginia.

Late on Tuesday, the Supreme Court denied her last-ditch appeal for a stay, and Ms. Lewis, now 41, is scheduled to die on Thursday night at 9. Her case has drawn unusual attention, not only because she would be the first woman executed in the United States since 2005, and the first in Virginia since 1912, but also because of widely publicized concerns about the fairness of her sentence. Ms. Lewis waited this week in her prison cell, reportedly soothed by intense religious faith.

Her lawyers say her original defense against the death penalty was bungled. They also cite new evidence suggesting that Ms. Lewis  whose I.Q. of 72 is described by psychologists as borderline retarded  was manipulated by her co-conspirators, who were out to share in savings and life insurance worth hundreds of thousands of dollars. Her partners in the crimes, two young men who fired the guns, received sentences of life without parole in what her lawyers call a “gross disparity” in punishment.

On Tuesday, blocking her only other chance for a reprieve, Gov. Bob McDonnell said for the second time that he would not grant clemency for what he called her “heinous crimes.”