"After having the baby, she got sick," she said. "She was depressed ... She was hospitalized."
Carey, 34, a resident of Stamford, Conn., led officers on a high-speed car chase that put Capitol Hill on lockdown and ended with her being shot dead by police. Her 18-month-old daughter, Erica, who was in the car with her at the time, was not injured.
Idella Carey said her 34-year-old daughter had "no history of violence" and that she didn't know why Miriam was in Washington on Thursday.
ABC News reported that her daughter was a dental hygienist. Her boss, Dr. Steven Oken, described her as a person who was "always happy."
"I would never in a million years believe that she would do something like this," he said. "It's the furthest thing from anything I would think she would do, especially with her child in the car. I am floored that it would be her."
The chain of events began Thursday when Miriam Carey drove her car past a set of barricades and sped onto a driveway leading to the White House. After she couldn't get through a second barrier, she spun her car in the opposite direction, flipping a Secret Service officer over the hood as she sped away, said B.J. Campbell, a tourist from Portland, Ore.
"This wasn't no accident. She was not a lost tourist," Campbell said later near the scene.
Then the chase began.
"The car was trying to get away. But it was going over the median and over the curb," said Matthew Coursen, who was watching from a cab window when Carey's car sped by him. "The car got boxed in, and that's when I saw an officer of some kind draw his weapon and fire shots into the car."
A Secret Service officer and a 23-year veteran of the Capitol Police were injured. Officials said they are in good condition and are expected to recover.
Rep. Michael McCaul, R-Texas, who was briefed by the Department of Homeland Security, said he did not believe Carey was armed. "There was no return fire," he said.
Thursday's incident comes two weeks after a mentally disturbed employee terrorized the Washington Navy Yard with a shotgun, leaving 13 people dead, including the shooter.
Police said Carey did not appear to have any links to terrorism. Capitol Police Chief Kim Dine, whose officers have been working without pay because of the government shutdown, called it an "isolated, singular matter."
Nevertheless, Congress suspended business as Capitol Police broadcast a message over its emergency radio system telling people to stay in place and move away from windows.
The FBI served a search warrant in connection with the investigation, and police cordoned off a condominium building and the surrounding neighborhood in Stamford as they looked for motives for Carey's actions.
Condo resident Eric Bredow, a banker, said police told him the suspect in the car chase was one of his neighbors.
"I see the door to my building open and the FBI bomb squad in front of it," said Bredow, who added that helicopters were flying overhead when he arrived home.