There are references in media stories about Muthana that say that after she left the US for Syria, she shared on social media a picture of herself burning her passport. What's unclear is what sort of consequences she could face.
Earlier this week, the British government revoked the citizenship of United Kingdom citizen Shamima Begum, who left the country at the age of 15 to join IS in Syria.
Muthana was born in 1994 in New Jersey to a father who had served as a diplomat from Yemen, according to her lawyer.
"During my years in Syria I would see and experience a way of life and the bad effects of war which changed me", she wrote in a letter that has been publicized by her family's attorney, Hassan Shibly.
"I would say that the situation of American citizens or possible American citizens in Syria is by definition extremely complicated, and we're looking into these cases to better understand the details", said State Department spokesman Robert Palladino in a press briefing on February 19.
Her family told James Longman, an ABC correspondent who's been sympathetic to Muthana, that she had a USA passport and was a citizen, indicating her passport may have been revoked.
"They're trying to say that she was never a citizen to begin with", Shibly said, attributing his knowledge of the government's claims to statements received by the family. Both of her terrorist husbands were reportedly killed in war. After he died, she married a Tunisian fighter and had her son Adam.
After leaving her Alabama home in 2014 to join ISIS in Syria, she became an outspoken advocate of violence against Americans, calling for bloody attacks on American soil.
"Americans wake up!" she tweeted after the death of her first husband, terrorist Suhan Rahman. After he was killed, she married another, the father of her son.
Muthana's father begged her to come back, to which he told BuzzFeed she replied, "I'm not going to come back".
But Muthana's lawyer says that she is a US citizen and holds a USA passport. Muthana's lawyer says the administration's position is based on a "complicated" interpretation of immigration law.
Shibly said she fled her family in Alabama and made her way to Syria, where she was "brainwashed" by IS and compelled to marry one of the group's soldiers.
Pompeo issued a statement declaring that she "is not a U.S. citizen and will not be admitted into the United States".
Her father, Mohammed, told BuzzFeed he gave his daughter a smartphone after she graduated from Hoover High School in May 2013. "I thought that I understood my religious beliefs, and I thought I had good friends, I stopped listening to my family and those who care about me and that was a big mistake".
"Please forgive me for being so ignorant", she recently told the Guardian, a British newspaper.
Trump's proclamation came just days after he warned European countries that they must repatriate and put on trial the 800-odd European IS fighters now held captive by the US' Syrian allies or the jihadists would be released, certain to "permeate Europe".
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