The home secretary will "robustly defend" the decision to strip Shamima Begum of her British citizenship, as European judges scrutinise the move, according to a government source.
The European Court of Human Rights (ECHR) has called for an investigation, but a government source said the the decision had already been upheld by UK courts.
Ms Begum was 15 when she travelled from east London to the Middle East, to a territory held by the Islamic State group, where she married a fighter.
Now 26, she was subsequently stripped of her British citizenship on the grounds that she posed a threat to national security but her lawyers say this failed to consider whether she was a victim of grooming and trafficking.
The ECHR has asked the Home Office whether ministers at the time considered whether Ms Begum had been a victim, and whether the UK had obligations to her.
