Foad is convinced that his sister Nora, whom he described as an impressionable teen who loved Disney movies before leaving for Syria one afternoon in January, stayed on because she was threatened with execution by the French-speaking commander, or emir, of the group she joined.
The former high school student is among dozens of European girls, many of them her age, living with such groups in Syria. It is an aspect of the conflict that is beginning to worry European governments previously more focused on the flow of young men to join the ranks of Islamic State and others.
Many of the youngest girls are lured with promises of humanitarian work. It is only once in Syria that they discover their fate: forced marriage to a fighter, strict adherence to Islamic law, a life under surveillance and little hope of returning home, say parents, relatives and radicalization experts.
"When she saw me enter that room, she couldn't stop crying and holding on to me. At one point I said, 'So, are you coming back with me?'" Foad, 37, told Reuters. "She started to bang her head against a wall saying, 'I can't, I can't, I can't.'"
Foad, who asked not to be identified by his full name to protect his family in France, said Nora had told him her first location was in Aleppo. He declined to give the location of their second encounter because he said French police had asked him not to reveal details relevant to investigations.
Foad said a conversation he overheard between his sister and the emir suggested she was warned to stay. Nora had repeatedly asked her family over the phone to be rescued from militants whom she called "hypocrites" and "liars".
While Western governments have focused on the thousands of male jihadist volunteers who have left to Syria and Iraq, security officials in Europe are expressing alarm about a smaller but steady stream of female groups heading the same way.
Making up about 10 percent of all departures for Islamist-held areas, according to government officials and terrorism experts, young women are seen as prizes for fighters keen to marry.
Teenaged Westerners are often targeted by older, female recruiters, many of whom are based in Europe and use social media, phone calls and false friendships to convince them to do charitable work in war-torn areas. Others need little convincing, keen to have a role in what they perceive to be jihad, or holy war.
A video recorded in secret by a woman in the Islamic State-held city of Raqqa in Syria and broadcast last month on France 2 TV gave a glimpse of the reality: women walking in burqas and one called to order by Islamic police for not adequately covering her face.
While women do not fight - although some form police units - their homes are near combat zones and exposed to bombing from coalition warplanes fighting the Islamic State. Women have little hope of escaping if they have regrets.
Austrian media reported that a girl of Bosnian origin, who left for Syria in April, had been killed in fighting. Reuters has not been able to verify the report.
Foad said all contact with his sister had been cut off since his May visit.
"Of the young women whom we follow, none have returned alive," said Dounia Bouzar, a French anthropologist in charge of a French mission to de-radicalize candidates for jihad.
As with other girls, Nora's embrace of radical Islam came as a shock to her family, which is not strictly observant.
Studious, sensitive and even childlike at home, Nora had a double identity including a mobile phone, Facebook account and Islamic garments that she kept secret from her family and which Foad only discovered after her disappearance.
"Her friends told me about the other Facebook account. When I connected, everything became clear: it was full of calls to jihad, of pictures of mutilated Syrian children," he said. "Three days later we got a message from her saying she was in Aleppo, that she was happy, well fed - as if she was in Disney World."
His quest to bring her home took him to Turkey's border with Syria, where he was taken in by Islamist militants and driven to a city he declined to name due to the sensitive nature of the information. The town was "full" of foreigners, each nationality having its own supply stores, including one area that was totally French-speaking, he said.
His sister currently lives with the close aide of an emir and was in charge of daycare for jihadists' children. She had earlier escaped a forced marriage arranged by a French recruiter who has since returned to France and is being held in custody.
Foad said his sister had identified the man as a Franco-Moroccan recruiter and former Al Nusra Front member, who returned to France in September and has been placed under formal investigation for various terror-related charges.
Severine Mehault, whose daughter Sarah disappeared from their home in southern France six months ago, said she believed her daughter, 17, also lived under strict surveillance.
"When we speak, it's always the same: 'I'm fine, I have everything I need, I'm not coming home,'" said Mehault, who last spoke to her daughter on Sept. 27 after 17 days of silence. "But I know somebody is listening, even writing in her place. The rare times she is alone, I can tell because her tone is different. She sounds like my daughter."
Security officials and radicalization experts say many women being radicalized hail from moderate Muslim households. But volunteers have also come from atheist, Catholic and Jewish households, both rich and poor, urban and rural.
"Recruiters have refined their methods to such a degree where they can take in people who are doing fine," said Bouzar. "Some are contacted on Facebook, others were chatted up on dating sites. Others met a friend who became a sort of guru."
Bouzar added that some of the women 'thought they were in love' after being groomed by men over the web or telephone - a trend also present in Germany.
"The romance of jihad is very pronounced in propaganda and used by women to recruit other women," Hans-Georg Maassen, head of Germany's domestic intelligence, said in a recent parliamentary briefing. "There is a real euphoria in the German Salafist (radical Islamist scene) right now, with people wanting to join this new state."
Of the 400 people who have left Germany for Syria, about 10 percent are women, he said. French officials estimate around 1,000 departures, with 60 of those being women. Of 85 jihadis who have left from Sweden, 15-20 were women, said Magnus Ranstorp, a terrorism expert at Sweden's National Defence College.
"They want to marry martyrs," he said. "There is almost an obsession with paradise and the afterlife, which makes it like a death cult. Death matters more than life."
"Women also become more revered. There is an internal hierarchy. If you become a widow, you become a mentor to the younger women and you would get status," added Ranstorp.
Bouzar - who follows 130 families concerned by the radicalization of their children - said her CIPD anti-radicalization group focused on stopping teens from leaving because the likelihood of getting a young woman back from Islamic State or other Islamist groups was nearly nonexistent.
Many French-speaking girls were housed together in an area controlled by the al Qaeda-linked Al Nusra front, she said.
"Some of them come to their senses over there," she added. "But that's almost worse than anything else, because they may be back to their old selves, but they are stuck over there."