Shamima Begum, the jihadi bride, was trafficked by ISIS for sexual exploitation, her lawyers have told a hearing to appeal against her deprivation of citizenship.
She launched her main appeal against the decision, with her lawyers telling a tribunal: "Shamima Begum is a young Muslim woman, someone about who everyone can give an opinion."
Samantha Knights KC, for Ms Begum, told the first day of a five-day hearing at the Special Immigration Appeals Commission (SIAC) that they faced an "overwhelming impediment" to make her case.
Her lawyers have compiled a series of experts to give evidence, including doctors and psychologists, who are experts in assessing how the adolescent mind affects judgment.
The appeal also heard from MI5, who said Ms Begum was an A-star pupil and it was "inconceivable" that she did not know what she was doing.
Dan Squires KC, for Ms Begum, said, in submissions: "It is clear that ISIS deliberately and successfully recruited underage girls for the purpose of sexual exploitation and in particular for the purpose of child marriage - which, under international law, is considered a forced marriage - and the bearing of children, which was an important feature of its state-building project."
Ms Begum was a "British child aged 15 who was persuaded by a determined and effective ISIS propaganda machine to follow a pre-existing route and provide a marriage for an ISIS fighter," Ms Knights told the tribunal.
Her transfer into Syria, across the Turkish border, was assisted by a Canadian double agent, her lawyer added.
Ms Begum, now 23, left Britain with two friends from the Bethnal Green Academy in East London, who are thought to have been killed in the conflict.
She was captured following the collapse of ISIS in January 2018 and taken to the al-Hawl detention camp, before being transferred to the al-Roj camp, where she has disavowed the terrorist group and said she wants to return home.
However, she was stripped of her British citizenship on the grounds of national security in February 2019 amid a political row over whether she was a dual British and Bangladeshi citizen.
Begum was 'cynically recruited and groomed'
Her lawyers also said Ms Begum was "cynically recruited and groomed" by ISIS so that she could be married off to an older man within days of arrival in their territory.
"The evidence is overwhelming that she was recruited, transported, transferred, harboured and received in Syria by ISIS for the purpose of sexual exploitation and marriage to an adult male - and she was, indeed, married to an adult, significantly older than herself, within days of her arrival in Syria, falling pregnant soon after," they said.
Ms Begum, who was 15 years old when she arrived in Syria, and "therefore not able to consent to marriage or sexual activity", was "married off" on or about February 20 2015 - 10 days after her arrival in Syria to Yago Reidijk, a Dutch national who was "considerably older," they added.
Ms Knights told the tribunal it is here that she is being "held in conditions of indefinite detention by a non-state actor, prevented from all access to her by lawyers and independent experts and, to her detriment, unrestricted access has been given to her by the press."
Home Office witness gives evidence
She called the case "extraordinary" and said Sajid Javid, the home secretary who deprived her of her citizenship, had taken "over hasty steps" less than a week after Ms Begum gave her first interview from detention in Syria to the Times.
Mr Javid then fed commentary, including an article written by himself, into the process, Ms Knights said.
"That is in direct contrast to the precautionary approach set out by our experts on how to assess the decisions, thoughts, and behaviour of an adolescent involved during her teenage years in a child marriage," she added.
The home secretary's duty to protect the public was not "monolithic" and required "wider context" as well as the consideration about the "safeguarding of victims" of trafficking, Ms Knights said.
Philip Larkin, a witness for the Home Office, told the hearing that there had been "no formal conclusion" on whether Ms Begum was the victim of human trafficking.
He accepted that Ms Begum must have had helped to cross the border, telling the tribunal: "Any individual who travelled illegally across the Turkish Syrian border would have needed assistance to make that trip."
But he declined to say whether she had been "recruited" was the victim of "sexual exploitation."
In July last year, the Supreme Court ruled against the Court of Appeal which had said that she should be allowed to return as the risk of her launching an attack could be "addressed and managed".
MI5: 'inconceivable' Begum did not know what she was doing
Witness E was asked whether the Security Service considered trafficking in their national security threat of Ms Begum and told the tribunal: "MI5 are experts in national security and not experts in other things such as trafficking - those are best left to people with qualifications in those areas.
"Our function was to provide the national security threat to the Home Office and that is what we did.
"We assess whether someone is a threat and it is important to note that victims very much can be threats if someone is indeed a victim of trafficking."
He added: "In our opinion it is inconceivable that someone would not know what ISIL was doing as a terrorist organisation at the time."
ISIS grooming the vulnerable
Shamima's lawyers said it was "well documented" that ISIS was "cynically grooming the vulnerable and young to join their movement," citing the government's own Strategy for Countering Terrorism from 2018.
The document said the government had a "well-organised online propaganda campaign" which involved using the internet to groom young people in the UK to travel to Syria.
Approximately 60 women and girls had travelled to ISIS-controlled territory, as part of a "campaign by Isis to target vulnerable teenagers to become brides for jihadist fighters", including 15 girls who were aged 20 years or younger, according to figures from the Metropolitan Police.
The victims of ISIS grooming included Begum's friend, Sharmeena Begum, who had travelled to ISIS-controlled territory in Syria as a child aged 15 on December 5 2014.
A girl aged 15 or 16, known as 'B', who also lived in the London Borough of Tower Hamlets, had attempted to travel to Syria but had been intercepted and taken off a plane whilst still in the UK.
The hearing continues.