Kimberly McCarthy, who is on death row in Texas for the 1997 killing of a neighbor during a robbery. Photograph: AP

Prison officials in Huntsville, Texas are preparing the death chamber for the state's 500th execution in the modern era, in this case of an African American woman who claims her trial was tainted by blatant racial discrimination.

Kimberly McCarthy, 52, has just hours to live as her lawyer attempts to persuade the courts to stay her execution scheduled for 6pm CDT Wednesday. On Tuesday night the court of criminal appeals of Texas declined to hear her appeal on grounds that the prisoner had exhausted all legal options to avoid death.

McCarthy's lawyer, Maurie Levin, was scathing about the appeal court dismissal, criticising the judges for being more concerned about "form over substance" even when a life was at stake. Levin, a law professor at the University of Texas, said the court's decision meant McCarthy would be executed "despite the fact that her conviction and death sentence were the result of a process that was infected by discrimination and race bias, and inadequate counsel appointed by the state. She will be executed despite the fact that no court has ever reviewed the merits of those claims."

Should McCarthy's execution go ahead the grim landmark of 500 executions since the death penalty resumed in 1976 following a supreme court review will confirm Texas's dubious distinction of being the undisputed champion of judicial killings. The state with the second most enthusiastic record for killing prisoners, Virginia, falls far behind with just 110 executions in the modern period.

McCarthy was sentenced to death in 2002 for the murder of her neighbour, Dorothy Booth, a retired college professor aged 71. McCarthy was at the time a crack addict and committed the stabbing during a robbery.

Her guilt has never been contested, but Levin has challenged the death sentence on grounds that she was consistently poorly represented by lawyers appointed by the state and that the jury at her trial that meted out the death penalty was racially manipulated. The case was racially charged from the start as McCarthy is black and her victim was white.

Of the 12 members of the jury, only one was black, despite the fact that almost a quarter of the population of Dallas County where the trial took place are African American. McCarthy's appeal for a stay of execution provides evidence that prosecutors consciously distorted the racial composition of the jury by rejecting three of the four non-whites who made it through to the final jury selection.

As the execution approaches, McCarthy's legal options will begin to close. Her last chance might be an appeal to the US supreme court, the highest judicial panel in the land, though it will take a powerful argument to convince the nine justices to consider the case.

Failing all legal intervention, McCarthy will be administered a massive dose of the barbiturate pentobarbital in a single lethal injection.

• This article was amended on 26 June to correct McCarthy's scheduled execution to Wednesday, not Thursday.