While living in then IS-occupied Mosul, Iraq, the 27-year-old German citizen identified only as Jennifer W. and her husband had purchased the child as a household "slave" in 2015, said prosecutors.

"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 of thirst in the scorching heat," they said in a statement.

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

The federal prosecutors said they had laid the charges of war crimes, murder and weapons offences back on December 14 in a Munich court that deals with state security and terrorism cases.

Jennifer W. had first left Germany in August 2014 and travelled via Turkey and Syria to Iraq where she joined the IS the following month.

Recruited to a vice squad of the militant group's self-styled morality police, she would later patrol the city parks of the IS-occupied cities of Fallujah and Mosul.

"Her task was to ensure that women comply with the behavioural and clothing regulations established by the terrorist organisation," said the statement.

"For intimidation, the accused carried an assault rifle of the type Kalashnikov, a pistol and an explosives vest."

In January 2016, months after the child's death, W. visited the German embassy in Ankara to apply for new identity papers.

When she left the mission, she was arrested by Turkish security services and extradited several days later to Germany.

For lack of actionable evidence against her, she was initially allowed to return to her home in the state of Lower Saxony.

"Since then her declared goal has been to return to the territory under IS rule," said the prosecutors.

When she attempted to again travel to Syria in June of this year, German police arrested her.

No date has been set yet for the start of the trial. If found guilty, she would face up to life in jail.