The mother, 25, who did nothing for more than four hours as her daughter's condition deteriorated, told the Newcastle District Court on Friday she questioned her actions on the day her daughter died every day.

She said she constantly asked herself, "why her, why my beautiful girl?" and was there something she could have done to help her daughter, before telling the court how she now suffered from depression, anxiety and nightmares.

It was later revealed the mother, who was found guilty in March by a Newcastle District Court jury of manslaughter due to criminal negligence, told a forensic psychiatrist she thought her daughter just "had some infection" on the day she died.

The mother denied having smoked cannabis before the murder.

The mother's partner, Timothy Whiteley, was found guilty by a jury of murdering the toddler in her bedroom and jailed in February for 35 years with a minimum of 24 years.

When sentencing Whiteley, Supreme Court Justice Stephen Rothman said it appeared, given the blood on the bedding and drawers, the first attack on the toddler occurred on the bed and there might have been a subsequent violent and forceful throwing of the child against a set of drawers. But it could not be said what had precisely taken place.

Justice Rothman said there appeared to be no motive for the attack except that Whiteley had earlier seen some suggestive text messages the mother had sent to his brother and he was stressed about losing his glasses.

The mother told her sentencing hearing on Friday how she had been subjected to online abuse since her daughter's death and was abused if she went to the shops.

"Losing my daughter is something I thought would never happen," she said.

"Not a day goes by when I don't think about (her daughter) and that day."

Whitelely, 29, told police he initially believed the girl had fallen out of bed and hit her head.

The toddler died from multiple injuries, including bleeding to the brain, six broken ribs, a collapsed lung, lacerations to her liver and bleeding in her abdominal cavity.

The girl had suffered a number of blows or kicks to the body.

Her bloodstained, size one pink Minnie Mouse pyjamas were later found in the bathroom.

The crown case against Whiteley was that he had been the only adult in the toddler's bedroom when she was attacked in a house in the Hunter region on June 19, 2018.

Whiteley claimed he didn't cause the girl's injuries or take part in the attack.

The toddler's mother also denied inflicting the injuries.

One key piece of evidence against Whiteley was the mother's claim that as Whiteley was performing CPR on the toddler before an ambulance was called, he said, "Don't you die on me, you little bitch."

Whiteley denied making the comment, claiming the mother was making it up to shift the blame for the girl's injuries away from her.

Whiteley and the girl's mother had been the only adults inside the house with the toddler when there was a loud thud heard by a visitor just before 12.20pm.

The toddler was carried from the bedroom area soon after by Whiteley in a clearly distressed state, unconscious and not responding but an ambulance was not called until 4.59pm.

The toddler was pronounced dead at 6.03pm at John Hunter Hospital.

The mother will be sentenced on June 23.

Australian Associated Press