Chyane Stephenson-Dielhenn, 18, and her 16-year-old accomplice, who cannot be named for legal reasons, held the victim hostage inside a 24-hour supported living facility in Barking and Dagenham for eight hours on 4 March.
While she was locked up, the victim was forced her to drink urine and swallow her own vomit. She was also tied up, punched and warned that she and her family would be killed if she tried to escape, Snaresbrook Crown Court heard.
The defendants – who the girl had considered friends – then posted footage of the harrowing ordeal on Snapchat.
Rather than raise the alarm, their followers suggested how they should torture her next.
During the five-day trial, prosecutors showed jurors clips, some filmed by Ms Stephenson-Dielhenn, of the “cruel and sickening attack”.
“The behaviour displayed was sadistic,” Elaine Cousins, from the CPS said.
“Stephenson-Dielhenn and her co-defendant egged each other on and took pleasure in controlling, humiliating and degrading the young victim. The victim was left understandably terrified and psychologically scarred.”
She added that the victim showed great bravery in reporting the attack and testifying in the case.
Passing sentence the judge Mr Recorder Shaun Murphy said the victim had been left “mentally and physically” scarred.
Ms Stephenson-Dielhenn, who denied false imprisonment and assault was sentenced to three years.
Her co-defendant, from Tower Hamlets, who had previously pleaded guilty to false imprisonment and assault occasioning actual bodily harm was jailed for two-and-a-half years.
Ms Cousins added: “I hope this conviction provides her with some comfort and makes clear that those who commit such vile acts will be prosecuted.”