Jenkinson and Eddie Ratcliffe, both now aged 16 but 15 at the time of the attack, were unmasked on Friday as the pair who stabbed Brianna to death in a “frenzied” knife attack near Warrington last year.
The teenagers, who face life behind bars, lured transgender Brianna, 16, to Culcheth Linear Park on 11 February;
Handwritten notes by Jenkinson, images of which have now been unsealed, have revealed how she planned the murder.
“Meet Eddie at wooden posts 1pm,” she wrote. “Walk down to library bus stop. Wait until Brianna gets off bus then the three of us walk to Linear Park. Go to the pipes tunnel area.
“I say code word to Eddie. He stabs her in the back as I stab her in stomach. Eddie drags the body into the area. We both cover up the area with logs etc.”
In others she has detailed notes on serial killers such as Jeffrey Dahmer, Harold Shipman, John Wayne Gacy and Richard Ramirez.
Dahmer, also known as the Milwaukee Cannibal or the Milwaukee Monster was a serial killer and sex offender who murdered and dismembered 17 young men and boys between 1978 and 1991.
Shipman was the British GP who murdered more than 200 of his patients, many of whom he injected with lethal doses of diamorphine, an opioid painkiller sometimes used for women giving birth.
John Wayne Gacy was an American serial killer who raped, tortured and murdered at least 33 young men and boys in Chicago in the 1970s.
Ramirez, a self-styled devil-worshipper was also an American serial killer nicknamed the “Night Stalker” who terrorised southern California in 1984-85, with a rampage of sexual assault and murder. He mutilated some of his victims and left Satanic symbols at some of the murder scenes.
Jenkinson and Ratcliffe were both jailed for life on Friday and given minimum terms of 22 and 20 years before parole.
The pair, previously identified only as girl X and boy Y, had denied murder and each attempted to blame the other for her killing, described as “horrific” by detectives.
Brianna’s parents told the sentencing hearing the pair should never be released from prison, with her mother Esther Ghey saying she felt her daughter’s killers still pose a danger to society.