The four siblings of a 20-month-old toddler murdered by his foster carer at a property outside Dubbo have revealed the lasting impacts of the death of their baby brother seven years ago.

The 45-year-old woman found guilty of murdering the boy appeared via audio-visual link in court on Wednesday, where she sat emotionless as the siblings of the infant described how the death had left a "hole inside of us all".

The eldest sibling explained she still had nightmares from her brother's death, and even suffers from crippling anxiety of leaving her children in the care of anyone but her and her husband.

She began to choke up as she described feeling responsible for the boy's death, revealing she had taken him to community services to protect him from extreme domestic violence they were enduring in their home.

"[In my dreams] I see an innocent baby being beaten and screaming for someone who loves him to save him. But no one helps and he is gone," she said.

"I wake up wishing I could have saved him like I tried to do, because the household we once called our family home had turned into us hiding in our rooms in fear of being hurt or our mum being hurt.

"I know with my whole heart I tried to keep my brother safe and I am not responsible for actions of murder performed on our innocent baby brother.

"I'll never heal from this and time does not make it easier."

The infant's brother was unable to finish reading out his statement, which said the incident had caused him to "fall apart".

"We missed out on doing brotherly things, playing football and running around getting into trouble like kids do," he said before his sister continued reading.

"We missed out on all the future possibilities.

"I had to leave school because I was getting suspended too much. I moved out of home and started drinking every day and bottling everything up, which led me to going down the wrong path. I got locked up for a day and that's when I realised all this has really affected me.

"I wish our brother went to a safe family, if he did he would still be here today with his family and we wouldn't be in this court room."

The foster mother was found guilty in February after a 17-day judge alone Supreme Court trial, which oversaw evidence presented from 26 witnesses and nine expert medical witnesses.

The 20-month old boy was found unresponsive at a property outside Dubbo, by paramedics on March 23, 2015, after the foster mother called triple-0.

The court heard the woman was unaware paramedics had answered the call when she was heard saying "they're going to think I bashed him", before asking "am I going to get in trouble for this?" when she called for help at 5.17am.

Despite multiple attempts to revive the child, he was pronounced dead at 7.30am at Coolah District Hospital.

Investigations found the boy had injuries to his bottom area and extensive bruising to his abdomen and face.

It was also revealed he had suffered a stomach rupture and a broken femur - the break so severe, it was compared to that sustained in a car crash. The child also was found with vomit in his mouth and on sheets.

The foster mother, who has three biological children of her own had given multiple, varying accounts to police of what happened on the night of the child's death.

In January 2018 the woman, whose name has been supressed by the court, was arrested in Geurie and charged with murder.

At a sentencing hearing on Wednesday the woman's defence barrister Janet Manuell SC asked Justice Richard Cavanah to take into account a number of subjective factors ahead of sentencing.

Two affidavits were tendered in court, which supported there was no suggestion the woman was anything other than a very good mother, during the five and a half months the boy was in her care.

"There's no history of the offender mistreating the boy in the days, weeks or months before his death, and to the contrary the evidence was that the offender continuously attended to the boy's needs," Ms Manuell said.

"All of the evidence was the offender was very good with the boy. That she fed him appropriately, that he was properly cleaned, properly clothed. She made changes to his diet, taking out sugar because of the impact it had on his behaviour. She took him to the doctor when she needed to, looked after him when he was unwell.

"The acts of violence must have been impulsive and spontaneous, there was no pre-planning. The acts were completely out of character, and there was no intention to kill.

"All of those combined make this a very unusual form of this offence."

Ms Manuell asked Justice Cavanagh to take into account the woman had "lost everything" since the boy had died.

"There is very little the offender hasn't lost," she said.

"She's lost the care of her children, her house, whatever assets she had, she speaks also of her personal possessions which were placed in storage and most of those haven't found their way back to her.

"She has lost the relationship with her grandmother who she was very close to, she has lost her social network."

She also highlighted the delay in the prosecution's case and the impact the COVID-19 pandemic had on the court process.

Ms Manuell argued this matter had been one of the most "extraordinary cases of forensic delay" that she had seen during her time as a barrister.

The woman was charged almost three years after the infant's death and as a result spent three years and five days in custody bail refused.

She was eventually granted conditional bail after a four week trial was delayed in November 2020.

Ms Manuell explained she was required to report to police daily, and did so almost 450 times, which demonstrated she was a "law abiding, honest and decent person".

She went on to argue the delays in the case could not be attributed to the offender, but rather the prosecution and COVID-19, and that it was an "extortionary situation" where a trial was listed to begin seven separate times.

"Beggars belief the stress that must have placed on the offender," Ms Manuell said.

The woman will return to court to be sentenced at a later date.