A court in Celle, Lower Saxony sentenced the girl to six years in prison on Thursday for attempted murder, grievous bodily harm and supporting a terrorist organization.
The girl, Safia S., had stabbed and severely wounded a 34-year-old police officer, reportedly as ordered by Isis, though the terrorist group did not claim it.
Safia S. had admitted to the attack and apologized to the officer while first in custody, as well as during the trial.
According to investigators, the teen student had flown to Istanbul in January 2016 in order to go from there to Syria with the help of Isis contacts. But her mother stopped her from travelling further and brought her back to Germany. She also reportedly had been in touch with Isis members online.
Prosecutors said the German-Moroccan national, who is believed to have been radicalized as a young girl, last February had sought to catch the attention of police officers by following them at the main train station in the northern city of Hanover.
As the officers called her over for an identity check, Safia S. allegedly stabbed one of them in the neck with a vegetable knife before being overpowered by another officer.
Prosecutors say the teenage girl was "motivated by members of Isis in Syria to commit this act".
A 20-year-old German-Syrian man was also sentenced to two and a half years prison because he knew about the girl's plans and did not report them to police.
Germany was hit by a series of jihadist attacks last year, with the deadliest occurring on December 19th when a Tunisian suspect rammed a truck into a crowded Christmas market in Berlin, killing 12.