A woman with infertility who was the “key architect” behind the murder of an intellectually impaired mother, so she could take custody of her four children, has been jailed for 30 years.

Christine Lyons, 47, previously had a hysterectomy but desperately wanted children of her own.

She had asked a number of women to have children for her, but no one agreed.

Finally, she put together a “heartless and thoroughly evil” plan to send 39-year-old Samantha Kelly “on a permanent holiday”, with the aim of taking custody of her children, aged between 11 months and six years.

Both Christine’s then-partner, Peter Arthur, and former lover, Ronald Lyons, were “so devoted” to her, they wanted to help her achieve her objective.

The trio lived together along with Ronald’s three children, with the “vulnerable” and “defenceless” Ms Kelly living in a bungalow at the back of the Bendigo home.

On January 20, 2016, Christine and Ronald Lyons fed Ms Kelly a cocktail of sedatives, beta-blockers, anti-nausea tablets, analgesics and antihistamines.

Ms Kelly felt groggy but did not die.

Then on the night of January 22 or the early hours of January 23, Christine – who has an IQ of 70 – directed Arthur to kill Ms Kelly with an “alternative method”.

Arthur then went to the bungalow and struck Ms Kelly with “extreme force” to the head with a hammer about seven times.

Ronald bought two shovels from Bunnings and accompanied Arthur on a trip to dispose of Ms Kelly’s body.