The woman, named as 35-year-old Omaima M., faces a slew of charges including membership of a foreign terror group, human trafficking and crimes against humanity.
She appeared before the higher regional court in Hamburg dressed in a blue blazer, using a magazine to cover her face from photographers.
Omaima M. is widely known in Germany for having been the wife of the late German-Ghanaian rapper and IS jihadist Denis Cuspert, who went by the stage name Deso Dogg.
Prosecutors said Omaima A. had travelled to Syria in January 2015 with her three children to join her first husband and their father, Nadar H., in Syria.
She lived under IS rules, raising her children following the group's doctrines, and receiving monthly financial help from the militant outfit, prosecutors said.
Between spring and summer 2015, Omaima A. allegedly held a 13-year-old Yazidi girl as a slave.
She married the rapper Denis Cuspert after her first husband was killed in an air raid in Kobane, according to prosecutors.
Cuspert was one of the most notorious Western fighters for IS, having appeared in several propaganda videos including one that apparently showed him with a man's severed head.
Omaima M. subsequently left Cuspert and returned to Germany pregnant with their child, as well as her three other children, in 2016.
Cuspert was killed in an airstrike in Syria in 2018.
Read also: Syrians face their torturers in German court, in huge step towards justice for Assad's victims
According to German media, Omaima A. quietly slipped back into German society after her return to Europe, working as an event manager and interpreter.
But a Lebanese journalist broke her story last year, sparking outrage in Germany over why she had not faced prosecution back in her home country.
Omaima M. was arrested in Hamburg last September.
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