She told the broadcaster: "I do feel that it's wrong that innocent people did get killed". "I thought I was doing things correctly for the sake of God", she added.
Shamima Begum was a British schoolgirl of Bangladeshi descent, who, with two other East London classmates, put together a packing list that seemed ordinary for any sleepover - makeup, bras, boots and an epilator - arriving in Turkey just three months after Muthana. In a letter to her family, seen by CBS News, she wrote, "I was a naive, angry and arrogant young woman... seeing blood shed up close changed me". But I don't regret it because it's changed me as a person. I don't understand what's gone on there.
Asked to respond to comments that she could be potentially very unsafe if she returned, she said: "They don't have any evidence against me doing anything risky. My beliefs weren't the same as theirs".
Terror researcher Seamus Hughes told CNN this week that Muthana had been a "key node" among English-language ISIS propagandists. "If she broke the law, then the justice system can deal with her, and if she didn't break the law, she should come back anyway, so it can be determined if she is a threat". "She was a key node". Two of her previous husbands, both ISIS militants, are also dead.
"Soooo many Aussies and Brits here, but where are the Americans, wake up u cowards", she posted in January 2015.
Muthana, who said she has not been contacted by us officials since her capture, said she hopes to return to America so she can reunite with her family.
Cressida Dick said the 19-year-old could expect to be "spoken to" if she comes back to Britain.
Now key questions remain - will she be allowed to return and can she readjust?
Some of her tweets were published in a Buzzfeed story, in which Muthana gave them exclusive access.
Shibly says Muthana was brainwashed and now could have valuable intelligence for US forces.
Muthana ditched her home in Alabama in 2014 to join ISIS in Syria, where she married several fighters and sent out tweets urging U.S. jihadis to "take down" President Obama and commit massacres at Memorial Day parades.
Have they forgotten Patty Hearst (the American heiress who was kidnapped by terrorists but then committed an armed robbery for them) or have they no awareness of the power of ISIL's fake news and propaganda on impressionable teenagers.
According to Muthana, she ran away from ISIS a few weeks ago and headed for the Kurdish area in northern Syria, where she is now in a camp for the displaced with her 18-month-old son. She could have her baby son taken from her. I don't know how, it's never been explained to me, ' " the newspaper reported.
She went on to write vivid calls over social media to kill Americans, glorifying the extremist group that for a time ruled vast swathes of Syria and Iraq.
But Hughes, the researcher, has words of caution.
Shibly, based in Tampa, Florida, said he intends to file a legal challenge to the government's decision to deny her entry to the country.