The paper said Smith, who spent two years in the Irish Air Corps during Bertie Ahern's tenure as Taoiseach, had met and married a British man in Syria who is believed to have died around two months ago.
In the ITV interview, Smith said that Isis' caliphate was "not over yet" but that supplies were running out in the group's last stronghold.
"The people don't have food. They're struggling, everything is expensive, so I don't know how they're going to keep living," she said.
"Morale is low, I suppose. Some are strong, it's like any roller coaster of people. Some want to leave, some don't. Some are hungry, some are not hungry. Some are tired, not tired."
She had previously spoken of converting to Islam in 2011, revealing she was previously a party girl who "did it all – the drink, drugs, smoking, everything".
In her ITV interview last week she said explained her desire to join Isis: "No music, no smoking, no fighting, no drinking, no prostitution ... you want a clean life like this, that is what you want, but sometimes it is not like this," she said.
The Irish Government said it was "aware of reports of an Irish citizen detained in northern Syria" but declined to formally confirm her identity.
The Irish police confirmed it was aware of an Irish woman "who left Ireland three or four years ago having become radicalised. She was previously a member of the Irish Defence Forces", but declined to confirm she was in custody.
The reported detention of Smith emerged amid cross-party criticism of Sajid Javid, the Home Secretary, after Kurdish officials confirmed that the 3-week-old baby of the teenage British jihadi bride, Shamima Begum, had died.
Diane Abbott, the shadow home secretary, blamed Javid's decision to remove Begum's citizenship for the child's death, accusing him of breaking international law and condemning the decision as "callous and inhumane".
Phillip Lee, a Tory MP said the decision had been driven by populism and that the British Government had failed in its moral responsibility to both mother and child.
"I was just troubled by the decision. It seemed driven by a sort of populism, not any principle I recognise," he told the BBC's Today programme.
The news of the death came as Begum's father Ahmed Ali offered an apology to the British public for his daughter's decision to flee the country and join the terror group.
Speaking from his home in the village of Dovroy, in north-eastern Bangladesh, he told the BBC: "She has done wrong, I apologise to everyone as her father, to the British people, I am sorry for Shamima's doing. I request to the British people, please forgive her."
Ali said added he only visited London three or four months at a time and had no idea how his daughter had become radicalised. He urged the British Government and public to "take her back and punish her if she had done any mistake".
Calm had fallen in the seige to take the last pocket of Isis' caliphate. Thousands of fighters and non-combatants remain inside the village of Baghouz, complicating plans to finally defeat the group, an SDF commander told the Sunday Telegraph.
Madani Ibrahim, an SDF field commander, said that intelligence gathered from surrendering Isis members this week suggests there are up 2000 fighters and 6000 women and children still living in the tiny triangle of land still controlled by the group.
"It there were no civilians it would take us three hours to finish all of this area. But there are civilians there and we don't want to make any mistakes, because the world's media will focus on the collateral damage," he said at a command post within sight of the Isil camp.
