Nada, 19, told MailOnline that US citizen Abu Abdullah al-Amriki (the American), 23, boasted about how beautiful women from all over the world wanted to join him in Syria and that he always kept a vial of poison on him - in case he was captured in battle.
She was bought by the ISIS emir - or local leader - at a slave auction in Islamic State's de-facto capital of Raqqa, Syria, in October.
The tall, pale man with black hair and short beard bought nine girls in total but sold seven of them on.
Nada was taken to one of his 'many' heavily-guarded houses in Manbij, Aleppo, where she lived with the other Yazidi girl and her son.
The teenager, who is now in America, told her harrowing story to the US government after escaping with her captor's phone. Her fellow Yazidi hostage, known as 'Bazi', is also in the country - she will give evidence against Abu Abdullah to Congress and wants the FBI to press charges against him.
MailOnline cannot independently verify these claims and Nada said she has never seen his picture before on videos or images released by ISIS.
She said Abu Abdullah was a very important figure in Islamic State and a stream of armed balaclava-clad militants from all nationalities visited the house.
She said: 'Many guests were coming and he was always explaining things to them. He was drawing maps of the fighting. He was telling everyone how to fight, about how to make an ambush.
'He was always ordering people to move and how to make a plan. He always carried a pistol and an AK47.
'There were also sniper rifles in the house, lying around. He also carried a policeman's stick which he used to beat me and the boy [another prisoner] with. He also slapped the boy.
'They didn't let me enter the room when they were talking. They only let me enter the room when they were talking tea to them.'
Nada described the wiry commander, who spoke Arabic badly, as a 'nervous' man who doused himself in strong perfume and yelled at her constantly.
He was so frightened of being captured that he always kept a vial of poison in his pocket, so he could commit suicide if his enemies ever took him alive. [...]
Posted by Women Against Shariah on Wednesday, September 30, 2015
From the Daily Mail: