Shamima Begum said she only wants to return to the United Kingdom with her newborn baby.
Earlier, Mohammed Tasnime Akunjee, a attorney for Ms Begum's household, told Radio 4's The World This Weekend: "They are obviously very satisfied and joyous that Shamima has efficiently given birth and that she's healthy".
British Jihadi bride Shamima Begum has reportedly been delivered of a baby boy in a refugee camp where she is taking abode in northern Syria.
The letter asked the mother to let her daughter know of the decision and to inform her she has a right to appeal.
But Lord Carlile, a former independent reviewer of terrorism legislation, said that under global law, Ms Begum would have to be accepted back into the United Kingdom if she had not become a national of any other country.
"I'm not the same silly little 15-year-old schoolgirl who ran away from Bethnal Green four years ago". She gave birth to a baby boy in a refugee camp in Syria, where a number of women are living after American and other forces decimated the Islamist terror group's presence in the region.
The case has reignited a debate in the United Kingdom about how to deal with citizens who joined ISIS but now want to return.
Ms Dick said: "This case and other cases that are talked about in the same sentences just really underline how bad the circumstances are and have been in Syria and just how risky it has been, and would continue to be, for anybody from this country to think of travelling there - unsafe physically and unsafe legally".
The head of Counter Terrorism Policing, Assistant Commissioner Neil Basu, said anyone returning from a conflict zone having gone to support a terrorist group should expect to face a police investigation.
"But I just want to come home to have my child".
In the same way Guantánamo Bay became a recruiting sergeant for extremism, cases like that of Begum will serve only to radicalise more young British Muslims.
Ms Begum, from east London, told the Times she feared her child would be taken from her if she returned.
He said that he is looking into different legal options.
She said Kadiza Sultana had died in a bombing on a house, but the fate of her other friend is still unknown.
Justice Secretary David Gauke said there were national security risks to allowing people such as Ms Begum to return to Britain but did not rule it out.
Metropolitan Police Commissioner Cressida Dick said the teenager would be spoken to by counter-terror officers if she were to return to the United Kingdom from Syria.
"I never did anything unsafe, I never made propaganda, I never encouraged people to come to Syria", she said.
British officials say about 900 Britons went to areas of Syria and Iraq that were controlled by the group.
If Ms Begum is ready to reach a British consulate in a recognised country, it's miles assumed security chiefs would possibly possibly "arrange" her return.
'She said she used to be a social worker and children of extremists, they get taken away, to the orphanage.'
"They are obviously very happy and joyous that Shamima has successfully given birth and that she's healthy", he said.