Victoria Osoteku, 20, was convicted of manslaughter and conspiracy to commit grievous bodily harm, The Guardian reported. Prosecutors said she used Facebook to organize the attack on Sofyen Belamouadden, 15, at Victoria Station in 2010 and was the only female involved.
"You played a pivotal role in the events of and leading up to that day and must take a substantial share of the responsibility for that," Judge Christopher Moss told her Thursday.
Osoteku testified for 21 days during her four-month trial. While she admitted she was at the station, she denied going there to kill the teenager or actively participating in the attack.
The jury was unable to reach a verdict on a murder charge.
Thirteen young people have received sentences ranging up to 18 years for murder. The attack apparently stemmed from disagreements between students at two schools.
The prosecutor, Mark Heywood, said the attackers went to the station in large numbers and heavily armed. He described the killing as "a truly terrible revenge" for a trivial insult.