Presiding judge Reinhold Baier of the superior regional court in the southern German city handed down the verdict to Jennifer Wenisch, 30, in one of the first convictions anywhere in the world related to the Islamic State group's persecution of the Yazidi community.

Wenisch was found guilty of "two crimes against humanity in the form of enslavement", as well as aiding and abetting the girl's killing by failing to offer help.

Wenisch and her IS husband "purchased" a Yazidi woman and child as household "slaves", whom they held captive while living in then IS-occupied Mosul, Iraq, in 2015, the court found.

"After the girl fell ill and wet her mattress, the husband of the accused chained her up outside as punishment and let the child die an agonising death of thirst in the scorching heat," prosecutors said during the trial.

"The accused allowed her husband to do so and did nothing to save the girl."

Wenisch's husband, Taha al-Jumailly, is also facing trial in separate proceedings in Frankfurt, where the verdict is due in late November.

Identified only by her first name Nora, the Yazidi girl's mother has repeatedly testified in both Munich and Frankfurt about the torment allegedly visited on her child.