Christine Mott of Leadville told The Associated Press that she was told of the arrest of her 31-year-old daughter in the case by the FBI and other federal law enforcement agencies.
She said that Jamie Paulin-Ramirez told her family after she left last September that she went to Ireland and married an Algerian whom she met online.
Irish authorities this week annnounced the arrest of seven Muslims in the alleged plot, only identifying them as three Algerians, a Libyan, a Palestinian, a Croatian and an American woman married to one of the Algerians.
They were arrested Tuesday, hours before U.S. authorities unveiled a terror indictment against Colleen LaRose, 46, of Philadelphia, who bills herself as "Jihad Jane."
LaRose is accused of plotting with others to kill Swedish cartoonist Lars Vilks because of his 2007 sketch depicting the head of the Muslim prophet Muhammad on a dog's body. The drawing provoked terror front Al-Qaida in Iraq to offer a $100,000 bounty for his slaying.
But on Saturday Irish police said that three of those arrested had been released without charges, while three other men and an American woman remain in custody.
Denver FBI officials say they can't confirm that the FBI had contacted Mott about the case. The U.S. Justice Department did not immediately return a call for comment early Saturday.
The Wall Street Journal, quoting anonymous sources familiar with the case, reported on its Web site that Paulin-Ramirez was being held in the alleged plot.
Christine Mott said she's concerned for the welfare of her grandson, who has been placed in the custody of Ireland's foster care system.
"This is about my baby," Christine Mott said. "We need some help to get this baby back. I'm concerned about my daughter but I'm concerned about our baby boy because he shouldn't be caught in the middle of this."