Shamima Begum, along with two schoolmates, fled her home in Bethnal Green, east London, in 2015 to join the terrorist group in Syria and marry its soldiers. She was 15 at the time.
Begum, now 19 and nine months pregnant, escaped Baghouz, the last bastion of ISIS's territorial power in Syria and Iraq two weeks ago, The Times of London reported .
She told the newspaper that she wanted to go home to London to protect her unborn child and because she believed ISIS's floundering self-styled caliphate "might not survive after all."
As the UK doesn't have a consulate in Syria, Begum would have to find her own way out of the region and make her way home. The British government has also warned that she could be questioned, investigated and prosecuted for terrorist offenses if she returns to the UK.
Sajid Javid, Britain's home secretary, also said he "will not hesitate to prevent" the return of people who left to support terrorist organizations abroad.
"I condemn anyone who has travelled to be part of this barbaric and brutal group," Javid told The Times on Friday, referring to ISIS, "and we must remember that those who left Britain to join Daesh were full of hate for our country." Daesh is an alternative name for ISIS.
He added: "My message is clear: If you have supported terrorist organisations abroad I will not hesitate to prevent your return. If you do manage to return you should be ready to be questioned, investigated and potentially prosecuted."
Ben Wallace, the British security minister, also said the government would not send troops into the region to rescue someone in her position.
"I'm not putting at risk British people's lives to go and look for terrorists or former terrorists in a failed state," he told the BBC's "Today" radio program on Thursday.
Unnamed security sources told The Times that Begum would be treated as a "national security threat" because she was one of the last people to leave ISIS's territory.
"These late returnees are the most dedicated to the ISIS cause, and therefore the most dangerous to us," one source told the newspaper.
Her family says shes harmless
As the government threatens to investigate and prosecute Begum if she returns, the teenager's family in Britain are insisting that she is not a threat.
Mohammed Rahman, the brother of Begum's brother-in-law, portrayed Begum as a victim and suggested that she supported ISIS's ideology as a result of Stockholm syndrome.
Rahman told The Times :"I can understand why people in this country are angry and don't want her back. What she's done doesn't portray Islam in a good light. But she was only 15 when she went to Syria. We are appealing for compassion and understanding on her behalf."
"She has been there [Syria] for so long, maybe the only way to make it through was to keep supporting [the ideology]," she added. "I can't imagine people get there and think, this is nice, I'd like to stay. So it's either [you] become depressed, or make something of the situation you are in."
Begum had described her life under ISIS as "normal," peppered with "every now and then bombing and stuff."
The father of one of the teenage girls who fled to Syria alongside Begum also said the girls "pose no threat."
Abase Huseen, the father of Amira Abase, told MailOnline : "These girls were young ... They were manipulated by evil people and they should be brought home and helped. Not punished. They pose no threat."
"Shamima should be allowed to come home and have her baby in peace," he added. "It was just a mistake that the girls left their families to go to a place like that."
Amira Abase's whereabouts are unknown. The third teenager, Kadiza Sultana, reportedly died in an airstrike in Raqqa in 2016.
