Three years on, the traumatized Yazidi is finally free of her captors, but remains trapped in a living nightmare, fearing the ISIS militants could still get to her, or worse, kill members of her family.
The frail 18-year-old former slave doesn't even know if her mother, father and brother are still alive.
At a meeting in the Kurdistan region of Iraq, she hides behind her cousin, one hand clenching her relative's shirt, the other holding tight to her own dress. Shell-shocked, she cannot remember how many younger siblings she has, and struggles to recall their names.
Nadia (not her real name) was among thousands of Yazidis captured by ISIS in August 2014 when the terror group launched an assault on Sinjar, then home to more than half a million members of this minority group.
In the days that followed, ISIS fighters split up families, executed the men and declared the women their slaves.
Nadia and and her older sister Amira were separated from the rest of the family. Their mother was pregnant at the time, and Nadia doesn't know where she - or her baby - is now.
The sisters were bused to several Iraqi towns like cattle, she recalls. They were taken to Mosul and locked up in one of Saddam Hussein's former palaces.
It was here, Nadia says, that she witnessed an incident that still haunts her: ISIS militants took a child away from his mother as she screamed for him. Her captors responded by hitting her on the head. Nadia still doesn't know what happened to the pair at the hands of the terrorists.
"They would tell us we sold you, we bought you," she says. "There were days we would wish we would die so no one says they sold us ... Beating and everything else is bearable, but not selling."
Collecting victims' stories
An Iraqi Kurdish investigator who asked to be identified as Shaima has heard stories like Nadia's dozens of times as she interviews freed Yazidis. "Some of them are eager to tell their story. Some of them are reluctant because they can't go into the details -- it's difficult for them," she says.
Shaima is a member of the Daesh Criminal Investigations Unit (DCIU), a team of Iraqi Kurdish and western investigators who have been operating secretly in Northern Iraq, for more than two years, collecting evidence of ISIS' war crimes.
The DCIU works for the Commission for International Justice and Accountability (CIJA), an organization based in Europe, its exact location kept secret for security reasons.
Their task in Iraq is dangerous -- the terror group remains at large despite losing most of the territory it once controlled.
"We will put the danger aside," Shaima told CNN. "The purpose we are serving is much bigger than to think about the danger."
Investigators have collected thousands of documents, phone records and videos left behind by the militants after they ravaged much of northern Iraq.
Earlier this month, CNN conducted exclusive interviews with the team in Iraq and toured its European office.
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