Ms Begum left Bethnal Green, in east London, aged 15 for Syria in February 2015, with two school friends in order to join ISIS.
Within days she had crossed the Turkish border and eventually reached the IS headquarters at Raqqa, where she married a Dutch convert recruit.
Since the fall of the Islamic State Ms Begum asked to return to the UK but had her Citizenship removed
Her citizenship was revoked by the Home Office on security grounds after she was found in a refugee camp in 2019.
The Court of Appeal has now said she had been denied a fair hearing because she could not make her case from the Syrian camp and that she should be allowed to return to the UK for her case to be heard.
The Home Office said the decision was “very disappointing” and it would “apply for permission to appeal”.