Christine Lyons, 47, was found guilty by a Supreme Court jury on Thursday of murdering Samantha Kelly, and of attempted murder over a failed attempt on her life days earlier.
But the killer’s former lover Ronald Lyons, who is not related to Christine, was cleared of murdering 39-year-old Ms Kelly.
Instead, he was convicted on the lesser charges of attempted murder and assisting an offender.
Ms Kelly, a disability pensioner, was struck repeatedly to the head with a hammer by Lyons’ current partner Peter Arthur in a bungalow behind their house in January 2016.
The Lyons were both found guilty of attempting to murder Ms Kelly with a cocktail of prescription and over-the-counter drugs before her eventual death at Arthur’s hands.
It was claimed the trio wanted her dead so Christine, who was infertile and "desperately" wanted kids, could take custody of Ms Kelly's young children.
The victim's aunt Tracey Lubcke was filled with emotion after the verdicts, expressing happiness and relief.
"Thank God!" screamed Ms Lubcke, who travelled to Melbourne from Ballarat for every day of the seven-week trial.
"I was starting to think I would have to bring in my bedding."
Ms Lubcke said her niece was a "gorgeous" but "vulnerable" woman who was preyed upon by her killers.
"She never saw the bad in people, even though they were horrible people," she said outside court.
Ms Kelly attended special needs schools as a child and still received support as an adult.
Ms Lubcke echoed what prosecutors said about the motivation for Ms Kelly's murder.
"She (Christine) wanted her kids," Ms Lubcke said.
"It was as simple as that. It's horrible."
In the lead-up to the murder, Christine and Ronald Lyons tried to give Ms Kelly an overdose of pills in her drink.
But when she was still not dead the next day, Arthur went to the bungalow and killed her with the hammer.
It was alleged Ronald Lyons bought two shovels and accompanied Arthur on a trip to bury Ms Kelly's body in a dry creek bed.
Arthur, 46, was jailed for 16 years but that sentence was later increased to 22 years on appeal.
Christine and Ronald Lyons will return to court for a pre-sentence hearing on August 15.