The teenager told an Iraqi Kurdish TV station that she was duped into going to Syria by her boyfriend last May.
She was rescued by Kurdish special forces near the city of Mosul a week ago, Kurdish authorities say.
At least 300 Swedes and thousands of other Westerners are believed to have joined IS in recent years.
In the interview with Kurdistan 24, the girl said she had met her boyfriend in 2014 after dropping out of school in south-western Sweden.
What is 'Islamic State'?
What life is like under IS in Mosul
"First it was good together but then he started to look at Isis videos and speak about them and stuff like that," she said in English, using the acronym of the previous name for IS.
"Then he said he wanted to go to Isis and I said 'OK, no problem', because I did not know what Isis meant or what Islam was - nothing."
Last year, when she was 15 and pregnant, the couple left the Swedish town of Boras and travelled through Europe by bus and train until reaching the Turkish border province of Gaziantep. From there, they crossed into Syria.
Then IS militants ferried them and other men and women by bus to the Iraqi city of Mosul, which has been under the group's control since 2014.
There, she said, they were given a house which had no electricity or running water.
"In Sweden we have everything, and when I was there, I did not have anything," she said in the interview, looking relaxed and healthy.
"I did not have any money either - it was a really hard life. When I had a phone I started to contact my mum and I said: 'I want to go home'."
Kurdish officials said on Tuesday that she was in the Kurdistan region of Iraq and would be handed over to Swedish authorities.
They said nothing about the fate of her baby, reportedly a boy.
A 16-year-old Swedish girl rescued from Islamic State (IS) militants in Iraq has described life under the jihadist group's rule as "really hard".