Mansfield grew up as a Baptist in Flint, Mich., worked for 10 years as a home healthcare worker, converted to Islam after marrying an Arab immigrant and went to Syria after they divorced, the Detroit Free Press reported.
Family members, who were questioned by the FBI Thursday, said they didn't know why she decided to go to Syria.
"She had a heart of gold but she was weak-minded," Monica Marie Mansfield, Nicole's aunt, said. "I think she could have been brainwashed."
A Syrian media outlet, Breaking News, portrayed Mansfield as an extremist and said government forces killed her this week.
Mansfield allegedly had grenades, ammunition and the flag of a group related to al-Qaida, Breaking News said.
Muna Jondy, a Syrian-American who is president of United for a Free Syria, an activist group in Flint, said the station is linked to the Bashar Assad government.