Christine Lyons, 47, was found guilty by a Supreme Court of Victoria jury in June of murdering Samantha Kelly, as part of a plan with her lover Peter Arthur to send the 39-year-old "on a permanent holiday".

Arthur is serving a 22-year prison sentence after he fatally struck the disability pensioner and mother-of-four to the head repeatedly with a hammer.

Christine Lyons was also found guilty of attempted murder over a failed attempt to kill her days earlier with a cocktail of prescription and over-the-counter drugs.

Her former lover Ronald Lyons, who is not related to her, was cleared of murder by the jury but convicted of attempted murder.

Ronald, 46, was also found guilty of assisting an offender after buying two shovels and helping Arthur bury the body in a dry creek bed.

On Wednesday, the Supreme Court of Victoria was told during a plea hearing that Christine had an intellectual disability, was "never able to escape poverty and disadvantage", and lived in a tent in a forest at one point with Ronald and his three sons.

Her defence barrister Peter Kilduff said Christine maintained her innocence and was currently in protective custody at the Dame Phyllis Frost Centre women's prison, where she spent her days untangling aeroplane headsets.

Christine had a hysterectomy in 2014 after suffering cancer and reportedly had a "powerful desire" to have a family.

Mr Kilduff argued Christine did "not strike the fatal blow" and that Arthur had an opportunity to withdraw from the agreement.

He said Arthur and was not working below Christine, "the matriarch", as part of a "pecking order".

Ronald's defence barrister Jarrod Williams argued his client's role "was somehow less involved".

But Justice Stephen Kaye described his conduct, including crushing pills into a drink as part of an attempt to murder Ms Kelly, as "absolutely deplorable" and "extremely heartless".

"The whole motive - it's evil, it's bizarre," he said.

"There's not even any relationship with Christine and yet he chose to join in."

In a victim impact statement read to the court, Ms Kelly's mother Vivien spoke of her grief at not having the chance to repair her relationship with her daughter.

"I wish I had been closer to her to protect her from you," the statement read.

"These thoughts haunt me."

Ms Kelly's brother Michael and his partner said they had taken custody of his sister's "four very traumatised children".

Justice Kaye described their actions as a "beacon for humanity" and a "self sacrifice...in raising these four beautiful children".

"May I commend most warmly what you and your partner have done for Ms Kelly's children," he said.

Christine and Ronald Lyons will be sentenced at a date to be determined.

Australian Associated Press