Ashwaq Haji Hamid had arrived in Germany in 2015 after spending 10 months in the Takfiri terror group’s captivity.
"I ran away from Iraq so I would not see that ugly face and forget anything that reminds me of it, but I was shocked to see him in Germany," she told InfoMigrants, a news site about migration.
"The first time was in 2016," she said. "He was chasing me. He was the same person, but the second time, he came close to me and told me he knew everything about me," she added.
In 2014, the group committed what the United Nations concluded was a genocide of Iraq’s Izadi community which Hamid hails from.
"If I had not seen him, I would have stayed in Germany. I wanted to complete my studies and get a degree that would give me a decent life," she said.
She said a friend of hers living in Stuttgart had told her a similar story about meeting her captor in Germany.
The police in the southern German state of Baden-Württemberg, who had been notified of the case, said the investigation could not progress further because the witness (Hamid) was unavailable.
Thousands of Europeans joined Daesh after it launched its campaign of bloodshed and destruction against Iraq and Syria in 2014.
The Arab countries and their allies defeated the group late last year.
However, a report published by the United Nations earlier in the week said between 20,000 and 30,000 Daesh terrorists had maintained presence in the countries.