Immigration and Customs Enforcement agents "did not target" the relatives of activist Erika Andiola because of her role with the Dream Act Coalition, the agency said in a statement provided to The Associated Press.
ICE officials also said Maria Arreola was released with an order of supervision, meaning she must check in periodically with the agency.
Andiola earlier said ICE agents told her that there was a long-pending deportation order for her mother, an immigrant from Mexico. Andiola questioned whether that actually prompted the arrest.
"They knew who I was and they know what I did," she said. "I'm really surprised that they came after my family because of the activism that I do."
Andiola's 53-year-old mother and a 35-year-old brother were arrested Thursday evening at the family home in Mesa.
Family members said the brother, Heriberto Andiola, was detained because he refused to answer ICE agents' questions.
The daughter said agents asked for her mother.
"The minute she got close to the door, they handcuffed her and they took her," the daughter said.
Heriberto Andiola was released early Friday, while the mother was released Friday afternoon after being returned to Phoenix from an immigration detention center in
Another brother, Angel Fernandez, said his mother told family members that she was on a bus to the border when the driver got a call and was told to return to Florence.
However, ICE officials said Friday that Maria Arreola was never on a bus to Nogales and she was returned to Phoenix from a staging area in Florence.
Before Maria Arreola was released, she was told she could remain in the United States for at least a year and might get a work permit, according to Fernandez. "She's pretty ecstatic right now," he said.
In releasing the relatives, ICE exercised its case-by-case discretion based on initial reviews, said ICE Press Secretary Barbara Gonzales, adding that "a fuller review of the cases is currently ongoing."
Immigration activists denounced the detentions, saying they showed a need for broad changes in immigration policy to end family separations.
"We cannot keep fixing this one worker, one family member at a time," said Marielena Hincapie, executive director of the National Immigration Law Center.