The 26-year-old was convicted alongside 43-year-old housemate Trudi Lenon at the Supreme Court of Western Australia in November.
Today, the pair were sentenced to life imprisonment with a minimum term of 28 years.
Lilley said she wanted to kill someone before she turned 25, and once she had ticked off murder from her “bucket list” she was so “full of herself and euphoric” that she could not help boasting to a work colleague, prosecutor James McTaggart told the court during a four-week trial last year.
She had previously written a book about a serial killer called SOS and went on to assume the identity of the character, the jury heard.
Speaking to The Times after the conviction, Lilley’s stepmother, Nina Lilley, 48, said: “The book was a big problem with me. At the beginning I was, ‘fair enough you want to write a horror story’, but I didn’t like the contents of it.
“She had always had an obsession with serial killers but she said it was a way of venting her frustration of what happened when she was a child.”
The victim – described by his mother as a “precious little boy” – was lured to his death on June 13, 2016, with both defendants blaming each other for the killing.
Lenon told the court Lilley approached the teenager from behind as he installed games on her computer, garrotted him until the wire broke then stabbed him three times.
The prosecution said Lilley left incriminating messages to her “obsequious and sycophantic” follower Lenon hours after the killing, saying she was feeling things she had “not felt before”.
After the verdict, the victim’s emotional mother Sharon Pajich told reporters she was heartbroken and would have to deal with what happened to her son for a lifetime.
His murderers were “disgusting animals” and should never be released, she said.
“He was my precious little boy, he was my first-born … he was full of life.
“[The killers] deserve everything they get for what they’ve done, they’ve taken an innocent boy from his loved ones.”