BRITTNEY Jade Dwyer will serve at least 21 years behind bars for the stabbing murder of her grandfather in a failed robbery that was influenced by a horror TV show.
Supreme Court Justice Kevin Nicholson sentenced the 20-year-old to life imprisonment with a non-parole period of 20.5 years for the murder of her 81-year-old grandfather Robert Whitwell at his Craigmore home in Adelaide's north in August last year.
She also received an additional six months for the home invasion - bringing her total minimum imprisonment to 21 years.
Her friend, Bernadette Burns, was sentenced to life imprisonment with a non-parole period of 13.5 years for the murder as she was found not to have murderous intent.
Both Dwyer and Burns' sentences were backdated to mid-2016.
After the duo drove from Queensland, Burns sat in the car outside Mr Whitwell's home applying her make-up while Dwyer stabbed her grandfather shortly after he had shown her family photos.
The girls were planning on robbing him of his life savings - $111,000, which was hidden in his shed.
Justice Nicholson described the offending as "evil" and "abhorrent", saying it was difficult to determine Dwyer's capacity for remorse.
He said Dwyer was influenced by her drug-taking, her inability to empathise, an unnatural interest in seeing people die and her greed for money.
"This murder was brutal, callous and cold-blooded," he said.
Last month, the court heard Dwyer was motivated by robbery but was also influenced by TV show American Horror Story.
Lawyer Craig Caldicott, for Dwyer, described that aspect as "very troubling".
Her mother Tonya Dwyer has previously said her daughter had an obsession with graveyards and "dark things" which set her on a macabre path.
She said her and friend, Shelby Lee Angie Holmes, both had a fascination with knives and violence in the lead-up to the murder.
"I think they are little bit dark, as in they would do things in cemeteries and go to cemetery tours and dark things," Ms Dwyer said.
"There were some things with blood and knives. I think they had a bit of an obsession with some dark stuff."
In April 2016, Brittney and Holmes, drove almost 2000km from Queensland to Adelaide to rob Mr Whitwell.
As Holmes was checking out the house, she sent text messages to Dwyer. One said: "He said hey to me omg he's lovely."
His granddaughter replied: "He is very lovely. Don't get attached to him. He might have to die."
The following day, the pair returned to the Craigmore home and failed in their attempt to rob him.
In early August, Dwyer again made the journey to Adelaide - this time with Burns.
Mr Whitwell started to show his granddaughter some photos of her and her brother as children and Dwyer decided she couldn't go through with killing him.
She sent a text message to Burns saying she was pulling out.
But Burns talked her out of it, saying her mother would know she'd visited her grandfather if she didn't go through with it and that she needed to "harden up".
As Mr Whitwell walked his granddaughter to the front door, she stabbed him in the neck, before he turned around and placed his hands on her shoulders.
She then stabbed him in the chest and again in the neck.
Bleeding profusely, Mr Whitwell asked his granddaughter why she had attacked him. She did not respond. He then walked to the kitchen and grabbed a band-aid.
Incredibly, Dwyer helped him apply the band-aid and handed him a cloth before she started washing the dishes as he passed away.
His body was discovered three days later and the killers were arrested on August 26.
In July, the court dismissed allegations made by Dwyer that her grandfather may have sexually molested her as a child.
The month before, Mr Whitwell's brother Geoffrey Whitwell spoke of his family's devastation at comforting Dwyer in the days after the death, before discovering his own granddaughter had killed him.
Holmes was given a 17-month suspended sentence for trespassing at Mr Whitwell's home in April.