Raelene Polymiadis, 65, is on trial in the South Australian Supreme Court, charged with murdering Brenda and Lynton Anderson, who were both aged 94 when they died in March 2022 and May 2023, respectively.
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 have told the court.
Major Crime investigating officer Detective Brevet Sergeant John Olive told the court on Tuesday he had applied for warrants for phone intercepts on Polymiadis' mobile phone and to place listening devices in her car and her Craigmore home.
Detectives had scrutinised hundreds of hours of recordings, he said.
A recording of a phone call between Polymiadis and her sister Faye Carruthers on June 2, 2023 - two days after Mr Anderson's funeral - was played to the court.
During a discussion about what happened after they arrived at Flinders Medical Centre following their father's admission, Ms Carruthers tells her sister: "I don't want you to get yourself so upset and stress over it."
Polymiadis replies: "That's the problem. I'm a storyteller, and I've written shitloads down, and it all sounds rehearsed, and it's too much information."
Prosecutor Michael Foundas has previously told the jury one potential motive for Polymiadis was a misplaced idea that killing her parents would spare them from going into a residential care facility.
Both had expressed a clear preference not to go into a nursing home and the prospects of that situation were looming large.
In the phone call between the sisters, Polymiadis says that after she told doctors at the hospital she was a diabetic, "he took a picture of my script on the phone".
"So they have got that. So that makes me think I'm in danger. But literally, it's just proving that I do what I'm saying," she said in the recording.
The trial continues.