The Government is set to ask for permission to appeal against a ruling that Shamima Begum should be allowed to return to the UK to challenge the deprivation of her British citizenship.
Ms Begum, now 20, was one of three east London schoolgirls who travelled to Syria to join the so-called Islamic State group (IS) in February 2015.
She lived under IS rule for more than three years before she was found, nine months pregnant, in a Syrian refugee camp in February last year.
Then-home secretary Sajid Javid revoked her British citizenship on national security grounds later that month.
In February this year, the Special Immigration Appeals Commission (SIAC) – a specialist tribunal which hears challenges to decisions to remove someone's British citizenship on national security grounds – found Ms Begum "cannot play any meaningful part in her appeal and that, to that extent, the appeal will not be fair and effective".
But SIAC ruled that "it does not follow that her appeal succeeds" and Ms Begum's challenge to the Home Office's decision to refuse to allow her to enter the UK to effectively pursue her appeal was also rejected.
However, earlier this month, the Court of Appeal ruled that "the only way in which she can have a fair and effective appeal is to be permitted to come into the United Kingdom to pursue her appeal".
Lord Justice Flaux – sitting with Lady Justice King and Lord Justice Singh – said: "Fairness and justice must, on the facts of this case, outweigh the national security concerns, so that the leave to enter appeals should be allowed."
The judge found that "the national security concerns about her could be addressed and managed if she returns to the United Kingdom".
Lord Justice Flaux also said: "With due respect to SIAC, it is unthinkable that, having concluded that Ms Begum could not take any meaningful part in her appeal so that it could not be fair and effective, she should have to continue with her appeal nonetheless."
He added: "It is difficult to conceive of any case where a court or tribunal has said we cannot hold a fair trial, but we are going to go on anyway."
The Government said it was "bitterly disappointed" by the ruling and Mr Javid said he was "deeply concerned" by the judgment.
The Home Office immediately announced its intention to seek permission to appeal against the ruling at the UK's highest court, an application which is due to be considered by the Court of Appeal on Friday morning.
Even if the Court of Appeal refuses permission, the Home Office could still renew its application for permission to appeal directly to the Supreme Court.
Ms Begum was one of three schoolgirls from Bethnal Green Academy who left their homes and families to join IS, shortly after Sharmeena Begum – who is no relation – travelled to Syria in December 2014.
Kadiza Sultana and Amira Abase, then 16 and 15 respectively, and Ms Begum boarded a flight from Gatwick Airport to Istanbul, Turkey, on February 17 2015, before making their way to Raqqa in Syria.
Ms Begum claims she married Dutch convert Yago Riedijk 10 days after arriving in IS territory, with all three of her school friends also reportedly marrying foreign IS fighters.
She told The Times last February that she left Raqqa in January 2017 with her husband but her children, a one-year-old girl and a three-month-old boy, had both since died.
Her third child died shortly after he was born.
The hearing, which will be conducted remotely via Skype, is due to begin at 9.30am on Friday morning.