Gardaí have arrested Lisa Smith on suspicion of terrorist offences following her return to Ireland this morning.
Her two-year-old daughter is being cared for by relatives, gardaí said.
The Islamic state supporter landed in Dublin airport with her daughter shortly after 10am.
She was handed over to the gardaí on arrival. Footage from RTÉ showed a woman, apparently Ms Smith, being escorted off the plane, covered by a blanket.
A spokesman for the Department of Foreign Affairs said the case “is now a Garda matter and the Department is limited in what it can say given that the person is being questioned by the gardaí.”
The Department said all Irish citizens in distress or danger overseas are entitled to consular assistance.
“Of primary concern to the government in this case was the welfare of a young child who was caught in the middle of a war zone.”
The Garda confirmed that a 38-year-old woman was arrested at Dublin Airport on suspicion of terrorist offences following her deportation from Turkey. She is currently being detained at a South Dublin Garda station under section 30 of the offences against the state act 1939.
The Minister for Justice, Charlie Flanagan, said established procedures for the care of Ms Smith’s child will be followed.
"An Garda Síochána and the Director of Public Prosections are responsible for criminal investigations based on facts and evidence in all cases and it would not be appropriate for me to comment on those matters. This is a sensitive case and I want to reassure people that all relevant State agencies are closely involved."
“A multi-agency network is in place here comprising agency personnel who engage on an ongoing basis with international colleagues regarding emerging practice in rleation to the complex issue of radicalisation. This network will coordinate engagement on a case by case basis as and when appropriate,” he said.
A small team of Defence Forces personnel flew to Turkey on Friday tasked with accompanying Ms Smith and her daughter back to Ireland on Sunday.
Tusla, the child and family agency, will now conduct an assessment of the needs and welfare of the child.
The Dundalk native and former Defence Forces member had been awaiting deportation in Turkey along with other supporters of the terrorist group who were captured by Turkish forces in Syria.
Ms Smith was accompanied on the flight by a small team of Government officials and members of the elite Army Ranger Wing.
On Friday Taoiseach Leo Varadkar refused to go into detail about the operation to return Ms Smith to Ireland. He said Tusla is playing a role in the matter, along with the Garda and Defence Forces.
"It is a tricky situation. Ultimately the child is an Irish citizen and deserves to be protected in my view. Ultimately we need to protect our citizens," Mr Varadkar told reporters at a graduation ceremony in Templemore for 197 new gardaí.
Mr Varadkar said there was a need to ensure the welfare of Ms Smith’s daughter. “Of course there are relatives that are in contact and Tusla are aware that situation may arise.”
Ms Smith is also an Irish citizen and has the right to return home should she wish, the Taoiseach added.
It is understood the Dundalk woman’s family members have expressed a willingness to care for her child in the event of her possible detention upon arrival in Ireland. However, any final decision would rest with Tusla.
Ms Smith had said in media interviews that she wished to return home. Mr Varadkar had previously said that a security assessment would need to be carried out to ensure that Smith “does not become a threat to life and limb in Ireland.”
The Irish Government has said for months that it has a responsibility to find a way to bring Ms Smith back to Ireland after she became aligned to the militant group in Syria and that its main concern was for the safe repatriation of her daughter.
Turkey says it has captured 287 militants in northeast Syria, where Turkish troops launched an offensive against the Kurdish YPG militia last month, and has hundreds more jihadist suspects in detention.
It began deporting foreign citizens linked to Islamic State earlier this month and Ireland confirmed shortly afterwards that Ms Smith and her daughter were the two Irish citizens identified by Ankara for deportation.
Turkey has accused its European allies of being too slow to take back their citizens who had travelled to the Middle East to join Islamic State.
Meanwhile, European countries are trying to speed up a plan to move thousands of jihadists out of Syrian prisons and into Iraq.