Maree Mavis Crabtree, 59, was in May found not guilty of the murder and attempted murder of her son Jonathan, 26, at the family's Gold Coast home in 2017.
She had also been accused of murdering her daughter Erin, 18, in 2012 but the charge was dropped during a review of the case in June.
Crabtree faced Brisbane District Court on Tuesday and pleaded guilty to two counts of obtaining financial advantage by deception by continuing to accept carer payments in late 2017 for another daughter, Tara, when they did not live together.
She also pleaded guilty to one count of fraud of at least $30,000 by accepting assistance payments from a disability organisation without declaring she had moved interstate.
Crabtree said "no" when asked if she had anything further to say after her guilty pleas.
She stood trial in the Brisbane Supreme Court in April accused of killing Jonathan by lacing his fruit smoothie with prescription painkillers on July 19, 2017, before making a $125,000 insurance claim.
In pre-recorded evidence, Crabtree's daughter Tara said she watched the hallway and kitchen while her mother crushed prescription painkillers and anti‑anxiety tablets as Jonathan lay passed out in bed.
Crabtree's defence attacked Tara's credibility due to her diminished intellectual capacity and potential to gain from her mother's jailing, while suggesting Jonathan could have suicided or accidentally overdosed.
The jury in May returned verdicts of not guilty to murder, attempt to murder and fraud after deliberating for nearly two-and-a-half days.
Crabtree spent six years on remand before her first trial ended in a mistrial in 2024 and she was granted bail.
She had claimed carer payments for Tara from after she was taken into care in August 2017 until shortly before Crabtree's arrest in January 2018.
Those offences were a more serious example of social security fraud, Commonwealth prosecutor Sunny van den Berg told Judge David Kent KC on Tuesday.
Crabtree also defrauded Lifestyle Solutions disability care organisation of almost $140,000 over four years.
She repeatedly lied to the organisation and said she was temporarily in Queensland, crown prosecutor Zachary Kaplan said.
But Crabtree's barrister argued the mother's time on remand had been quite onerous as she spent her entire time in protective custody and was incarcerated during COVID lockdowns.
"She has had to deal with the (deaths) of her two other children and had to grieve their loss while in custody," Susan Anderson said.
Crabtree was sentenced to one month in jail for the carer payment offences and ordered to repay more than $12,200 via her disability support pension.
She was convicted and not further punished for the state fraud offence.
Due to time served, Crabtree was released immediately.
She declined to comment as she left court.
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