The summary stated that Burns convinced Dwyer to do it because "they had come all this way".
"Ms Burns further said that the accused's mother would know she had been to her grandpa's and she should just 'harden up' and do it," it stated.
"Five to ten minutes later, [Dwyer] told Mr Whitwell she had to leave.
"As he walked towards the front door, she pulled out the knife she had brought with her and stabbed him in the neck.
"Mr Whitwell turned around and put his hands on her shoulders.
"The accused then stabbed him in the chest, and again in the neck."
Whitwell then asked his granddaughter why she was doing this but she did not respond.
The 81-year-old then walked into the kitchen and grabbed a band-aid, which his granddaughter helped put on one of his wounds.
"She washed the dishes while he passed away," the summary stated.
"The accused then sent a text message to Ms Burns saying 'it's done'.
The documents state that Burns then entered the house wearing gloves and the pair searched for Whitwell's money.
They took $1000 from his wallet, some coins, two digital cameras - but failed to find more than $110,000 was hidden in his shed.
His body was discovered three days later and the killers, who have pleaded guilty to murder, were arrested on August 26.
Dwyer and Burns drove from Brisbane to Adelaide to rob Whitwell.
The documents also revealed Burns posted on Facebook an hour after the murder: "the story of my life, I knew better but I did it anyway".
Jodie Greaves told police she and her partner, Jamie Dennis, lived with Dwyer and Burns until the murder.
She said after they had returned from their trip to Adelaide, Dwyer told them her uncle had died in Perth after a home invasion.
"I recall Jamie saying to her that was a bit random," she stated.
But she stated that Burns approached her and said, "can I tell you something, but you can't tell anyone other than Jamie?"
"She went on to tell me that her trip to Adelaide was for the purpose of robbing her grandad," she said to police.
"Bernadette said that before they set off on that trip, Brittney made a joke to her that she was going to kill her grandad, but Bernadette told me she didn't think she was serious at first.
"Bernadette told me when they got to Adelaide, Brittney told her that she couldn't do it.
"Bernadette told me she had a go at Brittney as she had spent all the money on fuel to get them to Adelaide and she then couldn't go through with anything.
"She went on to tell me that she sat in the car discussing things with Brittney for about 20 minutes and then Brittney changed her mind and went into her grandad's house.
"Bernadette said Brittney had her breakfast with her grandad and then she said she killed him.
"I asked her if she was joking and she said, 'no' and she burst into tears and started crying uncontrollably."
Both girls have pleaded guilty to murder and will face further sentencing submissions later this month.
The court has previously heard how the horrific crime has affected Whitwell's family, who comforted Dwyer in the days after the murder.
An accomplice to an earlier attempted burglary of Whitwell's house, Shelby Lee Angie Holmes, 19, was jailed for 17 months although the sentence was suspended.
