A woman obsessed with serial killers who murdered an autistic Perth teenager for the thrill of it has lost her appeal against conviction.

Jemma Lilley, 28, and her 45-year-old bondage-loving housemate Trudi Lenon garrotted then stabbed 18-year-old Aaron Pajich at their Orelia house in June 2016.

They wrapped his body, buried him in a shallow grave in their backyard, and covered it with concrete and red tiles.

Lenon, a mother of three, lured Mr Pajich to their house on the pretence of seeing her 13-year-old son to play computer games.

She had been a submissive participant in bondage, discipline and sadomasochistic role playing, and considered Lilley her "dominant", deriving pleasure from serving her.

For both, they perceived killing someone as the fulfilment of their shared violent fantasies, WA Court of Appeal Justice Michael Buss said in reasons for rejecting Lilley's challenge on Tuesday.

None of the grounds had any merit, Justice Buss said.

Outside court, the victim's mother Sharon Pajich said she was happy with the outcome.

"We're just going to move forward now ... that's the final chapter," she told reporters.

Father Keith Sweetman held back tears, saying he and Mr Pajich's stepmother Veronica Desmond were trying to get on with their lives but were not coping well.

Lilley, a supermarket shelf stacker, was 16 when she wrote a book called Playzone, which centred on a fictional serial killer named SOS, which stood for Son of Sam, a name she adopted in exchanges with Lenon and tattooed on herself.

She was a big fan of horror characters Freddy Krueger and Dexter, and had various macabre items around the house including a Chucky doll and a large number of knives.

Lenon, who used the nickname "Corvina" in messages with Lilley, had the younger woman tattoo SOS on her forearm the night before she was arrested.

She told Lilley in a text: "I will fear you, but respect you ... I am in awe."

The reply read: "100 per cent perfect."

When police went to the house, they had to force their way into a locked, tarpaulin-covered room where the window was covered in black plastic and a flattened-out shopping trolley with a board on it lay on the floor.

Lilley claimed she was preparing to paint the area before using it as a waiting room for her tattoo clients.

The pair bought large amounts of hydrochloric acid and plastic drums, with the prosecution alleging they were considering using them to dispose of Mr Pajich's body.

The women blamed each other at their Supreme Court trial, but a jury took less than three hours to find them both guilty in November 2017.

Both were jailed for a minimum of 28 years.

Lilley was moved to a regional prison after it emerged she was openly having a romance with neo-Nazi murderer Melony Attwood in a metropolitan jail.

Lenon suffered serious burns after a fellow inmate poured boiling water over her.