Tara Crabtree had claimed her mother asked her to "keep lookout" as she crushed up a fatal dose of drugs and put them in her brother's drink, later hearing her sibling struggling after he had consumed it.
The jury heard Tara told her friend to delete the last remaining copy of their latest conversations in Facebook messenger.
"You wanted (your friend) to delete messages about the death of your brother? defence barrister Angus Edwards said.
"Only to keep her out of this," Tara said.
Tara said her friend had obsessive compulsive disorder around germs and would not want her phone "contaminated" by police touching it.
Maree Mavis Crabtree is accused of killing her 26-year-old son Jonathan with an overdose of painkillers on July 19, 2017 in the family's home north of the Gold Coast before making a $125,000 insurance claim.
The 59-year-old has also been accused of attempting to murder her son in January that year.
Crabtree pleaded not guilty to murder, attempted murder and fraud charges when her trial began at Brisbane Supreme Court last week.
The jury on Friday began watching nearly five hours of video evidence from the accused's daughter Tara that was pre-recorded this week.
Tara said she was one year younger than Jonathan at the time he died, and living with him and Crabtree.
The jury heard Tara claimed Crabtree crushed up prescription painkiller and anti-anxiety tablets while Jonathan was passed out in bed.
"She cut up fruit and put it in the blender to blend it ... watermelon, pretty sure mango, pineapple are the main ones I remember," said Tara, who has immunity from prosecution.
The jury previously heard Jonathan co-owned the family home and could not be evicted despite being verbally and physically aggressive to Tara and Crabtree after suffering a brain injury in a car crash.
Under cross-examination, Tara said she had repeatedly told "half truth, half lies" about the likelihood her brother took his own life in the two years after he died.
Tara said she loved the family's five-bedroom home that she part-owned but had heard her mother had received money to try to take her name off the deed.
Mr Edwards asked Tara if it was true she told police that she wanted to change her story two years after the fact as she believed her mother was trying to take their house.
"I was mentally stable and able to talk to them (police)," Tara said.
The jury was shown text messages in which Tara was asked by a friend about the possibility her mother would paint her as a liar and escape conviction.
"I honestly do not care if she does that," Tara said in April 2021.Â
"In the end I have the house."
Tara said Crabtree crushed up tablets with a hammer and added the powder to the fruit smoothie along with six bottles of liquid oxycodone opioid painkiller.
"She asked me to keep lookout for my brother. He came out and she gave it to him," she said.
Crown prosecutor Caroline Marco asked Tara why Crabtree had put drugs in Jonathan's smoothie.
"We would have more peace and live a better life without him, that's what she said," Tara said.
She said she had heard Jonathan struggling and making noises after he returned to his room with the smoothie but Crabtree told her not to interfere.
Tara testified that Crabtree feared she would be arrested and "lose everything" and Tara would be forced to live in a group home if Jonathan survived.
The jury also heard Tara claim she and Crabtree were concerned about Jonathan killing them at some point though his violent behaviour.
Tara said she was in "shock" after Jonathan died and Crabtree told her not to say anything if the police arrived.
"He committed suicide, that's what she told me to say," Tara said.
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