The 37-year-old defendant, identified only as Nadine K., is also facing charges of crimes against humanity and membership of a foreign terrorist organisation before a court in the southwestern city of Koblenz.

Federal prosecutors say Nadine K. travelled with her husband in December 2014 from Germany to the IS-controlled part of Syria where they joined the jihadist group.

Months later the couple and their daughter settled in the Iraqi city of Mosul, the former "capital" proclaimed by IS, where they allegedly hoarded weapons and established a hostel providing room and board for "single female members" of IS.

"From early 2016, Nadine K. and her husband kept a Yazidi woman as a slave," prosecutors said when she was charged in September. "The man raped and beat the woman regularly, which Nadine K. knew."

They said Nadine K. kept watch to prevent the woman, who was 22 at the time, from fleeing and forced her to do housework and care for children while observing Islamic rituals.

"All of this served the declared purpose of IS, to wipe out the Yazidi faith," prosecutors said.

Nadine K. and her family are believed to have moved to Syria in autumn 2016 with their "slave" and lived in IS-controlled territory until March 2019, when they were believed to have been arrested by Kurdish fighters and the Yazidi woman released.

The defendant was arrested last March upon her return to Germany in one of several repatriation operations.

A German court in November 2021 issued the first ruling worldwide to recognise crimes against the Yazidi community as genocide, in a verdict hailed by activists as a "historic" win for the minority.

The Kurdish-speaking Yazidis hailing from northern Iraq have for years been persecuted by IS militants who have killed hundreds of men, raped women and forcibly recruited children as fighters.

Last May, a German woman who joined IS in Syria as a teenager was handed a two-year suspended prison sentence but cleared by a court in Naumburg, central Germany, of aiding and abetting crimes against humanity.