Lisa Cunningham

This Sunday 7News Spotlight speaks exclusively to an Aussie mum accused of the unthinkable.

Did Lisa Cunningham kill her seven-year-old stepdaughter Sanaa, or was her death a medical tragedy?

In her first on-camera interview, Cunningham speaks candidly from inside a maximum-security prison in Arizona about the devastation of losing her family and the impact of eight years' incarceration without trial.

Lisa said, "It's always been such a mystery to us why it is easier to believe that we tried to slowly kill her with this bizarre, delayed death torture story than it is to simply accept the fact that she entered into the early onset period of serious mental illness."

The alleged killer details the final 10 months of her stepdaughter's life, a time in which prosecutors claim she and her husband, Germayne, subjected Sanaa to abuse that ultimately caused her death.

The exclusive story also features never-before-seen family videos and text messages that prosecutors claim prove their case, texts that Lisa says don't tell the full story.

"If you look at our lives from a distance and you go through our messages and the way we communicated with each other, you are going to form your own opinions," Lisa said.

Reporter Ashlee Mullany said: "The story of Lisa Cunningham is confronting whichever way you look at it. This is either a case of an Australian mother accused of an unthinkable crime, or a woman unjustly stripped of her freedom, family and voice for eight years.

"I covered Lisa's first court appearance after her arrest in Arizona almost a decade ago and what should have been her temporary holding cell has become her home for all these years, without conviction. The wheels of justice turn slowly, but this has been an agonisingly long wait for answers.

"Lisa is adamant she has nothing to hide and wants to share her story with Australia."