Khadiza Sultana, 17, is thought to have died after her home was destroyed by a bomb that was believed to have been dropped by a Russian plane.
ITV News reveal that Sultana became disillusioned with life in the medieval terror state and was making plans to flee back to Britain.
The schoolgirl and two friends Amira Base and Shamima Begum left their families in east London during the Easter school holidays in 2015.
Base and Begum, who were both just 15 when they fled, are believed to still be in Raqqa.
The trio became some of Britain's most infamous ISIS recruits and shocked the nation after leaving their A-Level courses and their families to marry fighters in Syria.
Sultana 's family were hoping to help to get her out of Raqqa and across the border into Turkey. But it is believed Khadiza was killed before she could flee, after the property she was staying in was obliterated by the airstrike in May.