Queensland mother accused of attempted murder of her baby says she was "possessed".

A Queensland mother claimed she was possessed and “attacked by the devil” when she allegedly tried to kill her baby daughter on three separate occasions, a trial has heard.

Ashleigh Meagan Watterson has pleaded not guilty to the attempted murder of four-month-old Sarah, who suffered “catastrophic” brain injuries when she was deprived of oxygen in late 2010.

Sarah died in March 2012 from unknown causes that are not part of the allegations against Watterson.

The Brisbane Supreme Court heard on Monday that Sarah was first taken to hospital by paramedics on October 28, 2010 after her mother called triple-zero stating she was “purple and had blood coming from her nose”.

Watterson claimed she left the child for less than a minute with her apnoea monitor turned off when she returned to find her blue.

On the same day Sarah was discharged Watterson again called for paramedics after her daughter stopped breathing, allegedly during the five minutes she was left alone.

It was during that episode Sarah suffered severe brain damage from a lack of oxygen.

In the final incident, Sarah was at hospital when Watterson allegedly arranged a “Do Not Resuscitate” plan with doctors before taking her child into a bathroom and tried suffocating her.

Prosecutor Danny Boyle said a man in the parents' lounge would testify to seeing a woman come out of the toilets with a baby in her arms saying: "I tried to kill my baby, it's just breathed".

Mr Boyle said medical experts could not find a natural reason for Sarah to have stopped breathing and Watterson deliberately obstructed her airways on each occasion, however this was never directly witnessed.

The court heard Watterson allegedly later confessed to police in August 2013, a month after she was charged with attempted murder.

"She wasn't having any apnoea events, that was me," Watterson said.

"I feel that the devil attacked and made me do things.

"I was possessed."

Mark Watterson testified his then-wife also confessed to him after she spoke to police.

"She told me she was responsible for Sarah's brain injury, that her hands did it but she didn't," Mr Watterson said.

Watterson's defence team will argue those confessions were false and brought on at the time by an undiagnosed mental disorder.

The trial continues.