The girl was being held by the militants with her 17-year-old aunt, but by drugging them into a deep sleep, both women managed to escape.
They found safety in nearby, Kurdish held territory.
The story was confirmed by Vian Dakhil, the only Yazidi member of the Iraqi parliament, who has been honored for her commitment to raising awareness of the group 's plight.
She said the two girls were held at a house in Tel Afar, near Mosul, for nearly four months before they made their escape.
They apparently did so by asking the ISIS fighters for pills to help them sleep.
Dakhil told Kurdish BasNews: 'Then, they put the medicine in militants’ tea and secured their escape after they fell asleep. '
The girl has been reunited with her mother and sister, but two of her siblings are still being held by ISIS militants.
The Yazidi group are an ethno-religious minority with ancient roots in Iraq, who have been persecuted by ISIS for being 'infidels ' since 2014, when the fighters surrounded their homeland of Mount Sinjar.
In addition to killing Yazidi men, the UN believe ISIS are holding around 3,500 women and children as slaves in horrific conditions, often deprived of food and water.
Women are subjected to sexual slavery by ISIS, something they justify on account of the group not being Muslim. Girls as young as 12 are sold for sex, or given to fighters as rewards.
Those who refuse to submit are often killed, in addition to older women who ISIS feel serve them no use.
Said Mamuzini, a Kurdistan Democratic Party (KDP) official from Mosul, also told BasNews: 'At least 250 girls have so far been executed by ISIS for refusing to accept the practice of what they call sexual jihad, and sometimes the families of the girls were also executed for rejecting to submit to IS 's request, ' Daily Mail reported.