Shamima Begum, who travelled to Syria eight years ago to support IS group, has lost the initial bid to challenge the removal of her British citizenship at the Supreme Court.
The government stripped Begum's citizenship on national security grounds in 2019, leaving her stateless.
Last year, she lost her first appeal against the decision to revoke her citizenship at the Special Immigration Appeals Commission.
The 24-year-old had recently requested permission from the Court of Appeal to take her case to the top court.
Dismissing her Court of Appeal, the Lady Chief Justice Baroness Carr, said, “The only task of the court was to assess whether the deprivation decision was unlawful. Since it was not, Begum’s appeal is dismissed.”
She may now ask the Supreme Court directly for permission to have her case heard.
Begum's lawyers have argued that British officials have failed to properly consider whether she was a potential victim of trafficking.
Born in the UK to parents of Bangladeshi heritage, Begum left for Syria in 2015 with her friends Kadiza Sultana and Amira Abase.
Sultana reportedly died when a house was blown up, while Abase's whereabouts is not known.
Begum married a Dutch member of IS, currently held in a Kurdish detention centre.
They lived in Raqqa, and the couple had three children, all of whom have died.
She was found in al-Roj camp in northern Syria in 2019 and still lives there.
