A 22-year-old woman who came to the United States from Argentina as a 7-year-old child and was allowed to remain in the country under an Obama-era program was detained by immigration authorities after speaking at a news conference in Mississippi about her fears of being deported, her lawyer said on Thursday.

The woman, Daniela Vargas, was picked up on Wednesday when the car she was riding in was pulled over by officers shortly after leaving the news conference at City Hall in Jackson, Miss., the lawyer, Abigail Peterson, said in a telephone interview. The event was organized by lawyers, church leaders and the Mississippi Immigrants Rights Alliance to raise awareness about the impact deportation and President Trump’s immigration policies have on families.

An officer placed Ms. Vargas in handcuffs after telling her, “You know what we are here for,” Ms. Peterson said. Ms Vargas was taken into custody and transferred to a detention center in Louisiana, where she was being held on Thursday without bond.

Ms. Peterson said the authorities informed her on Thursday that Ms. Vargas would be processed as a “visa waiver overstay,” which means she would not be given a hearing and would be flown to Argentina.