The case against Jennifer W., 27, is believed to be the first anywhere in the world for international crimes committed by IS militants against members of the Yazidi minority.

The defendant faces life in jail if found guilty of committing murder and of murder as a war crime, as well membership in a terrorist organisation and violations of the German War Weapons Control Act.

Nobel Peace Prize Laureate Nadia Murad, herself a Yazidi survivor of IS enslavement and torture, said the Munich trial "is a very big moment for me, and for the entire Yazidi community".

Prominent London-based human rights lawyer Amal Clooney is part of the team representing the dead Yazidi girl's mother, although Clooney was not expected to appear in the Munich trial on its opening day.

- 'Agonising death' -

German prosecutors allege Jennifer W. and her IS husband had "purchased" the Yazidi child and her mother, a co-plaintiff in the trial, as household "slaves" whom they held captive while living in then IS-occupied Mosul, Iraq, in 2015.

"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 charge.

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

German media said the defendant's husband, Taha Sabah Noori Al-J., had beaten both the Yazidi mother and child, and that Jennifer W. allegedly also once held a pistol to the woman's head.

The trial is being held under tight security in a Munich court that deals with state security and terrorism cases, with hearings initially scheduled until September 30.

- Morality police -

Jennifer W., who reportedly left school after the eighth grade and converted to Islam in 2013, travelled in mid-2014 from Germany via Turkey and Syria to Iraq where she joined the IS.

Recruited in mid-2015 to an anti-vice squad of the group's self-styled hisbah morality police, she patrolled city parks in IS-occupied Fallujah and Mosul.

Armed with an AK-47 assault rifle, a pistol and an explosives vest, her task was to ensure strict IS rules on dress code, public behaviour and bans on alcohol and tobacco consumption.

In January 2016, months after the Yazidi child's death, Jennifer 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 at the time, she was allowed to return to her home in the German state of Lower Saxony, but quickly sought to return to IS territory.

- FBI informant -

Der Spiegel reported that an FBI informant posed as an accomplice who offered to take Jennifer W. back to the IS "caliphate", chatting with her in a bugged car while they drove through Germany, headed for Turkey.

Jennifer W. allegedly said that the child's death had been "hard-core even for the IS" and unjust because only God had the right to use fire as punishment. Her husband had later been beaten as punishment by the IS, she said.

Police followed close behind her vehicle for several hours and listened to a live audio feed as Jennifer W. spoke and then arrested her at a highway stop.

Clooney, the wife of Hollywood star George Clooney, has been involved in a campaign with Nadia Murad to get IS crimes against the Yazidi minority recognised as a "genocide".

"I hope that this will be the first of many trials that will finally bring ISIS to justice in line with international law," the lawyer said in a statement, using an alternative acronym for the group.

The IS targeted the Yazidi community in Iraq and Syria through an organised campaign of executions, enslavement, sexual violence and forced recruitment of child soldiers, forcibly displacing hundreds of thousands from their homeland in Iraq.