The horrors Mediha Ibrahim Alhamad experienced during her three years of Islamic State captivity is something she will never forget. She was just 10 when she was kidnapped from her home in Sinjar, in northern Iraq, in the summer of 2014, and sold into sexual slavery among IS fighters. Yet when she was released, she felt “nobody would listen to me”.

Mediha, now 19, has since found solace in film after she was given a camera by the US documentary film-maker Hasan Oswald, who she met at a camp for internally displaced people (IDP) five years ago, while he was reporting in the region. She started telling her family’s story, as well as documenting the challenges she faced after captivity – a process she says “saved my life”.

“When nobody would listen to me and I was told not to talk about what I went through, the camera became my only friend. I found that when I spoke to it and confided in it, I would instantly feel better, like a weight lifted off of me. I used the camera, and now the film itself, to heal in many ways. It was my outlet and it remains so,” says Mediha.

Her footage has been turned into an award-winning documentary, Mediha, which has its UK premiere this week.

The documentary, executive produced by actor Emma Thompson, opens with shots of the IDP camp in Iraqi Kurdistan where Mediha lived with her uncle and two of her brothers after she was rescued from captivity in 2017. It includes footage of her parents’ wedding. “Like most of the men, he is probably dead,” Mediha says to camera about her father, Ibrahim. “That’s my mother, Afaf. Look how beautiful she is,” she adds. Her mother is still missing.

Mediha’s childhood ended in August 2014 when IS militants attacked her village, Tal Qasab, in Sinjar, the heartland of the Yazidi people, and took her entire family captive. It was an event that garnered global attention, and became one of the darkest episodes of IS brutality in Iraq and Syria.

More than 3,000 Yazidis, a persecuted minority, were killed, and nearly 7,000 kidnapped to become soldiers or slaves, and tens of thousands displaced. About 3,000 women and children are still missing.

Mediha was separated from her parents and three brothers and sold into sexual slavery among IS fighters.

At one point during her captivity, despairing of ever being rescued, she says she wished she could marry one of her captors and “have kids and then be like other [IS] women, rather than a captive”. “I thought it would allow me to be free … More than anything, I didn’t want to keep being resold, and I thought that would give me some stability and safety. Sexual abuse was the worst part of captivity, of course – I was so young. Now I think back and I just thank God that I didn’t get pregnant.”

Mediha was rescued after the city of Mosul, an IS stronghold, was liberated by coalition forces. She was initially arrested because she had been forced by IS to carry a gun and wear a suicide vest. She was taken to an IDP camp and reunited with two brothers and her uncle.

Oswald, the documentary’s director and co-producer, says handing the camera to Mediha helped address “the balance of power between film-maker and subject”.

While Mediha shot her footage and video diaries, Oswald filmed those trying desperately to locate and rescue Yazidi captives. One scene shows a rescuer looking through conversations on messaging apps. He finds one that reads: “slave for sell 12 years old not virgin very beautiful in raqqa … $13,000 letzter preis!! [final price].”

“Today, little to nothing is being done in terms of rescues,” says Oswald. “As our film was finishing up, we witnessed the last resources dry up and pretty much all rescues stopped. There is no national or international effort to return the missing, and very little is being done in terms of helping the survivors. Most of the efforts come at a local level through NGOs and private groups.”

One emotional scene in the documentary, which was awarded the grand jury prize at the DOC NYC film festival in November, shows the moment Mediha and her two brothers, who were rescued before their sister, are reunited with their youngest brother, Barzan. He was sold as an infant for $120 to an IS family with no children. Barzan is crying and asking Mediha to be allowed to go back to his “mother” – the IS woman who brought him up for five years. Mediha holds Barzan in her arms under a blanket, trying to comfort him.

“I want to show and tell the world what happened to my people and what is still happening,” Mediha says.

“I want to inspire other girls in the region to speak out. Not just Yazidi girls but also girls who have gone through something similar and are scared to tell the world what happened to them.”

She also hopes that the film will help find her mother. “I have a faint wish and hope that my mother is still alive and that maybe someone will recognise her in the film and tell her that we are alive,” Mediha says. “I know she would be proud of this film and of me. If she is alive, I know she would come home if she knew her children are alive and well.”

• Mediha opens the Human Rights Watch film festival at the Barbican in London on 14 March. It will also be available to stream on the festival website from 18 to 24 March.