Despite having a "credible" claim that she was trafficked, Shamima Begum lost her appeal against the decision to strip her of her British citizenship.
Her appeal had been completely rejected, Mr. Justice Jay informed the somewhat secret court hearing her case.
The 23-year-old is now stuck in a camp in northern Syria and cannot leave; as a result of the decision.
When Ms. Begum left to join the so-called Islamic State organization in 2015, she was 15 years old.
After marrying a fighter from the group, she went on to have three children, all of whom have passed away.
She lost her British citizenship in 2019, when Sajid Javid was the home secretary, preventing her from returning home and keeping her detained in a camp as an IS supporter.
The Special Immigration Appeals Commission has ruled that the decision, which was made after ministers were informed of Ms. Begum's threat to the UK due to national security concerns, was lawful despite the fact that her attorneys had made a compelling case for why she was a victim.
Watch the documentary on BBC iPlayer while listening to The Shamima Begum Story podcast on BBC Sounds.
Ms. Begum's attorneys claimed during the appeal hearing in November of last year that the decision had been unlawful because the home secretary had overlooked the possibility that she had been a victim of child trafficking. In essence, they claimed that Ms. Begum had been groomed and duped into joining the fighters along with her schoolmates. .
"The Commission concluded that there was a credible suspicion that Ms Begum had been trafficked to Syria," Mr. Justice Jay said in a summary of the decision.
"Sexual exploitation, to which she was unable to give a legally binding consent because she was a minor, was the reason for bringing her to Syria.
"The Commission additionally came to the conclusion that there were questionable derelictions of duty on the part of various State bodies in allowing Ms. Begum to leave the country in the manner in which she did, ultimately crossing into Syria from Turkey. ".
Despite these reservations, the judge ruled that the home secretary's legal obligation to decide whether to deprive Ms. Begum of her British citizenship did not change even if she had been a victim of human trafficking.
"There is some merit to the argument that those advising the secretary of state see this as a black and white issue, when many would say that there are shades of grey," the judge concluded in his summary.
However, despite these concerns about how the case had been handled, the Commission came to the conclusion that the home secretary had still acted within his authority - even though there might have been a different result.
The judge stated that if given the task of weighing all the relevant evidence in Ms. Begum's case, "reasonable people with knowledge of all the pertinent evidence will differ, particularly with regard to the issue of the degree of her travel to Syria being voluntary and the weight to be given to that factor in the context of all others.".
She posed a threat to the national security of the UK in February 2019, and reasonable people will disagree about how that threat should be weighed against all other relevant factors.
However, according to our constitutional arrangement, the secretary of state, not the Commission, is responsible for assessing these delicate matters. ".
Although it's not yet known if Ms. Begum will file an appeal, a spokesman for the Home Office said the department was "pleased" with the result.
The spokesman said, "The government will vigorously defend any decision made in doing so. Maintaining the safety and security of the UK remains the government's top priority."
