It's not just being alleged by anonymous people.
Who then, Nancy Mace who Trump call 'crazy' and a 'terrible person' in 2022.
It would be easy enough to prove by checking her and her father's citizenship records. Based on what I have read, when Ilhan's father became a U.S. citizen in 2000, she automatically became a U.S. citizen, 'derivative citizenship. This was when she was 17 years old. So, there was no need for her to be married to a U.S. citizen, much less to her brother.
As of early 2026, Ilhad Omar remains a U.S. citizen, and no federal, court-verified proof has been produced to invalidate her 2000 citizenship status.