Killer mum whose son suffered an agonising death covered in bruises and vomit is DEFENDED by her ex-partner in court - who says she was a 'good mum when she was stoned'

A Gold Coast mother fighting to have her sentence reduced for killing her four-year-old son was 'indifferent' to his suffering, a court has been told.

Heidi Strbak, 37, has served almost three years of a nine-year sentence for the manslaughter of Tyrell Cobb.

In March, Strbak's sentence was set aside after a successful High Court appeal and she is being re-sentenced in the Brisbane Supreme Court.

Tyrell died on the Gold Coast in May 2009 after Strbak and her then de-facto Matthew Scown failed to seek timely medical treatment for the sick boy.

Heidi Strbak (pictured with her son Tyrell Cobb), 37, has served almost three years of a nine-year sentence for the manslaughter of her young boy

The pair were convicted of manslaughter in separate trials.

Tyrell had been vomiting bile for two days following a blow to his abdomen, which tore open his small intestine.

An autopsy revealed 70 bruises and abrasions, as well as a cigarette lighter burn on his ankle.

During a four-day contested sentencing hearing, the court heard Strbak had been frustrated and angry before Tyrell's death, asking the boy's father to take his son as she 'couldn't handle' the toddler.

Scown also gave evidence Strbak did not seek medical help for Tyrell on the day he died, fearing accusations she had 'bashed' him.

He said the couple regularly smoked cannabis together and Strbak became 'frantic and panicky' when she wasn't using the drug.

'When she was stoned she was a good mum,' he told the hearing.

Tyrell vomitted bile for two days following a blow to his abdomen, which tore open his small intestine

In closing submissions on Friday, the Crown argued Strbak did not seek medical help for Tyrell because she was responsible for inflicting the blows.

'Her son is vomiting green bile and covered in bruises and she doesn't go anywhere near any physicians - that is a remarkable position for a mother to have taken over the course of that weekend,' Philip McCarthy QC said.

'The explanation is that she knew she bore some responsibility.'

He said Strbak was 'indifferent' to Tyrell's suffering and disguised its seriousness.

In closing submissions on Friday, the Crown argued Strbak did not seek medical help for Tyrell because she was responsible for inflicting the blows.

'The breach of trust and the departure of the standard of care expected of a mother to protect and care for her son - particularly in the position of this child's dependency and vulnerability on that weekend is egregious,' Mr McCarthy said.

'It remains difficult to comprehend.'

Defence barrister Saul Holt said there was no dispute that the injuries to Tyrell were unlawful and intentional, but Strbak was not responsible.

Justice David Boddice is expected to reserve his decision.