Death row Briton Linda Carty has said she will not stop fighting for the truth until she proves her innocence.
Carty, 51, could be given the lethal injection within weeks after the US Supreme Court refused to review a murder conviction campaigners said resulted from a "catastrophically flawed" trial.
In a speech written for the opening of a life-size death row cell in central London, Carty said: "As a mother and a grandmother, I cannot give up hope of being free to hug my grandchildren again."
Carty was convicted in 2002 over the kidnap and murder of Joana Rodriguez, who was seized alongside her four-day-old son by three men on May 16 2001. The baby was found unharmed in a car, but Ms Rodriguez was killed, having suffocated with duct-tape over her mouth and a plastic bag placed around her head.
Carty's speech launches an exhibition which runs to September 5 and includes a replica of her death row cell in the courtyard of St Martin-in-the-Fields church in Trafalgar Square, central London. A film of Carty speaking about her imminent execution will play on a loop, and visitors will be encouraged to write and post a letter in a special post-box asking the Texas authorities to spare her life.
"I am scared - sometimes I'm so scared I can't even speak," she said. "My words alone can't prove my innocence. That will require a fair trial and thorough examination of the evidence showing how and why I could never have committed the terrible crime of which I've been accused.
"But I can simply speak against murder itself. I believe that the truth will come out one day, that my innocence will be proven. But 'one day' takes on a whole new meaning when you are staring death in the face. I haven't got time on my side. As an innocent woman, I will not stop fighting for the truth."
Carty claims she was framed over the murder by the men who carried out the abduction due to her earlier work as an informant for the Drug Enforcement Agency.
Legal action charity Reprieve claim Carty was given an incompetent defence lawyer during the original trial who, amongst other alleged failings, neglected to inform the British Government so it could intervene on her behalf. The Foreign Office complained of "ineffective counsel" in court filings it made under the last government in support of Carty.
But in May, the US Supreme Court refused an application to review the murder conviction. It means that Carty could be executed unless the Governor of Texas intervenes.