Her prayer, captured on a police listening device in her car, included her saying "thou shalt not kill" before adding: "they did not want to go to a nursing home", a jury was told.
The secret recordings were played on Thursday at the South Australian Supreme Court trial of Polymiadis, 65, who has pleaded not guilty to murdering her elderly parents with insulin.
Brenda and Lynton Anderson died in March 2022 and May 2023 respectively. Both were 94 at the time of their death.
The jury on Thursday were played audio from a police listening device hidden in Polymiadis' car, recording her as she drove to the Elizabeth police station to be interviewed by Major Crime detectives on June 20, 2023.
"Please, Lord, you know, yes, I have sinned. I have. Thou shall not kill," she allegedly says.
"I have sinned twice in my life, and I hate it, but I also know ... your blessing, Lord, that they did not want to go to a nursing home, that was their wish."
Mrs Anderson died from an insulin overdose at the Flinders Medical Centre.
Mr Anderson also died at Flinders Medical Centre, after he was found unconscious on his kitchen floor with a large amount of insulin in his body.
Polymiadis, a type 1 diabetic with access to insulin, had been the last family member to see each parent before they became unwell, prosecutors told the court.
A police search of her car after the interview uncovered handwritten notes that detectives allege were written by Polymiadis.
One note reads: "What they will do is wait for a few weeks, months, year (sic) to see if I 'think I got away with it' and I get cocky and slip up.
"Hang on buddy, it could be a long ride, otherwise the suspect would be arrested now."
Another note about visiting Polymiadis' father in hospital states: "just holding his hand, talking to him, but I got no response (sob)".
A third note poses a series of questions, including "Who are you sorry? What's this about? Are you from the Coroner's office? Why only now are you speaking with me and it's only a few days after the funeral!!"
In the interview with police, Detective Brevet Sergeant John Olive told Polymiadis he suspected she had knowledge of the circumstances of her parents' deaths.
"What?" she replied.
"I've got no idea about this."
Asked if she wanted a lawyer present, Polymiadis said: "Common sense would tell me, shit, if you're accusing me of this, do I need help? Because I didn't do it."
Defence counsel Marie Shaw KC has told jurors context and interpretation were issues with the alleged confession.
In the same prayer, Polymiadis says: "God, they've got into my stuff, and it's all my fault."
"Was my client admitting she was responsible for this, or was she telling her God that she felt responsible for their deaths?" Ms Shaw said in her opening submissions.
"Because if they died of insulin administration, they must have accessed her insulin."
The trial before Justice Sandi McDonald continues.
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