The mother of a victim in the abuse complex in Münster is said to have been imprisoned for seven years and nine months after a ruling by the regional court for aiding and abetting by omission.
The judges were convinced that the mother knew that her then partner had sexually abused her son severely.
The now 32-year-old did not prevent the rapes, it said in the verdict on Wednesday in Münster.
The court is thus below the demands of the public prosecutor's office, which had asked for a prison sentence of ten years.
One of the defense attorneys had spoken out in favor of a six-year prison term, another had given no sentence.
The woman had surprisingly made a partial confession before the pleading.
On the penultimate day of the trial, she admitted that she had considered the abuse possible since October 2019.
But she was not able to end the relationship.
In her last word, the mother expressed her regret.
At the start of the trial in early August, she had still denied the allegations.
Stepfather is seen as the mastermind in the abuse complex
Most of the proceedings - in order to protect the now twelve-year-old victim - took place in camera.
The stepfather, an IT technician, is considered to be the mastermind in the complex, which revolves around the rape of children in a gazebo in Münster and other places in Germany.
The man was sentenced to 14 years imprisonment and subsequent preventive detention in the main trial.
Alongside Lügde and Bergisch Gladbach, Münster is one of three major abuse complexes in North Rhine-Westphalia in recent years.
The case came to light in June 2020 after investigations into a gazebo.
In the course of this, there had been arrests in several federal states and abroad.
Several men and one woman have already been sentenced to imprisonment in the offense.