Shamima Begum "in some respects...would have known what she was doing" when she travelled to Syria as a teenager to join a terror group, an MI5 officer has told a court.
Ms Begum, now 23, was 15 when she and two other east London schoolgirls travelled to join the so-called Islamic State group in February 2015.
Her British citizenship was revoked on national security grounds shortly after she was found, nine months pregnant, in a Syrian refugee camp in February 2019.
Ms Begum is challenging the British Home Office's decision to remove her British citizenship, with her lawyers arguing that the department had a legal duty to investigate whether the then-teenager was a victim of trafficking when the decision was made.
On the first day of a five-day hearing at the Special Immigration Appeals Commission (SIAC) - where a proportion of the proceedings are expected to be in private - an MI5 officer only known as Witness E gave some evidence in public.
Dan Squires King's Counsel (KC), part of Ms Begum's legal team, asked the officer whether they had discussed talking to a trafficking expert while considering Ms Begum's case.
Speaking from behind a screen, the officer said they could not answer the question publicly, but later said it was "worth remembering the context" of the terrorist organisation's acts around 2015.
The officer said the groups' actions around the time included large terror attacks and the public beheadings of multiple people - including journalist James Foley and aid worker Peter Kassig in 2014.
"It is inconceivable someone would not know what ISIL (Islamic State) was doing as a terrorist organisation at the time," they continued.
The witness noted Ms Begum was predicted high grades in her exams, suggesting she was "intelligent", "articulate" and likely capable of critical thinking".
They added: "In some respects yes, I do think she would have known what she was doing and would have had agency in doing so."
Witness E later said that MI5 are experts in national security threats, not trafficking.
"We consider whether someone is a threat and it is important to note we recognise that victims can be threats if someone is a victim of trafficking," they added.
At the start of today's hearing, Samantha Knights KC, also for Ms Begum, said the woman had been "persuaded, influenced and affected with her friends by a determined and effective ISIS propaganda machine".
In written submissions, Mr Squires and Ms Knights said Ms Begum's case was a "paradigm example of child trafficking for the purposes of sexual exploitation and forced child marriage".
"She was following a well-known pattern by which ISIS cynically recruited and groomed female children, as young as 14, so that they could be offered as 'wives' to adult men."
Her lawyers said that the Home Office deprived Ms Begum of her citizenship "without seeking to investigate and determine, still less consider, whether she was a child victim of trafficking and whether there were failures by public authorities in the UK to prevent her being trafficked".
"What evidence is available shows that rather than viewing the appellant as a victim, a child that was manipulated and exploited, the Home Secretary proceeded on the basis that she acted 'voluntarily' in travelling to Syria and aligning with ISIS," the lawyers added.
James Eadie KC, for the Home Office, said in written submissions that the Security Services "continue to assess that Ms Begum poses a risk to national security".
"This is a case about national security," he said, later adding: "This is not a case about trafficking."
He said that Ms Begum "travelled, aligned and stayed in Syria for four years" and that she only left IS-controlled territory for safety reasons "and not because of a genuine disengagement from the group".
He continued: "When she did emerge, and gave multiple press interviews shortly before the Secretary of State decided to deprive her of her citizenship, she expressed no remorse and said she did not regret joining ISIL, acknowledging that she was aware of the nature of the group when she travelled."
The hearing in London marks the second part of Ms Begum's SIAC case, following a ruling in February 2020 that the Home Office did not unlawfully leave her stateless by revoking her British citizenship.
The hearing before Mr Justice Jay is due to finish on Friday with a decision expected in writing at a later date.