A pregnant teenager who watched as her ex-boyfriend was tortured to death was an "amoral facilitator of serious violence", a judge said.
Chelsea Platt, 18, lured Martin Hyde to her flat in Stockport, where her two friends severely beat him, Manchester Crown Court heard.
He was then taken to a park where he was stabbed through the neck, leaving him paralysed, and thrown in a river.
Platt pleaded guilty to conspiracy to commit grievous bodily harm.
The court heard how she knew her friends James Dellaway, 24, and Jason Hughes, 28, wanted to attack 22-year-old Mr Hyde over an unpaid £15 debt to Dellaway's girlfriend.
Mr Hyde, who was homeless, had also reported the pair to police over a previous assault.
Dellaway, of Hollywood Towers, and Hughes, of Hardman Street, both pleaded guilty to murder.
On Wednesday, they were sentenced to life and must serve a minimum of 25 years and 73 days before being eligible for parole.
Platt, of Brecon Towers, was sentenced to four years in a young offenders institute.
Platt had grown contemptuous of Hyde and months earlier had sent him a Facebook message which read: "You need to die really badly because no one likes you."
In November, she invited him to her flat on Brecon Court, Stockport, where he was repeatedly punched, kicked and stamped on by Dellaway and Hughes.
The court heard that he was also hit with a frying pan three times and forced to mop up his own blood with a sponge before being then gagged with it.
Platt then followed the men as they took him about a mile away to Reddish Country Park, where he was stabbed repeatedly.
His spinal cord was severed by one wound and he also suffered significant brain damage as a result of some of the 72 separate injuries.
Mr Hyde's half-naked body was found two days later.
Sentencing the three, Mr Justice Ryder said: "A crime of the gravest severity was committed against a defenceless young man.
"Those responsible should know that society views their actions with the utmost revulsion.
"You knew why it was happening, You facilitated the process of bullying and violence."
The court also heard that Platt had set up her ex-boyfriend for beatings on other occasions
"You are a reprehensible, amoral facilitator of casual and serious violence," Mr Justice Ryder told her.
Dellaway's girlfriend, Lindsay Dunn, 20, of Hollywood Towers - also heavily pregnant - and Peter Mayne, 18, also of Hollywood Towers, both admitted conspiracy to commit grievous bodily harm.
Both were witnesses at the river bank and both punched Hyde before he was thrown in the river.
Dunn was sentenced to four years detention in a young offenders institute. Mayne must serve 18 months.
Speaking after the hearing, Det Ch Insp Jon Chadwick, of Greater Manchester Police, said: "It was the most brutal and sustained attack I have witnessed in my career and visibly shocked my staff.
"All of these people share responsibility for his death, irrespective of who actually inflicted the horrible injuries he sustained.
"They all played a part and none gave a thought to trying to help him."