Authorities said the woman set off a high-speed car chase that put the Capitol on lockdown Thursday and caused a fresh panic in a city where a gunman killed 12 people two weeks ago.
Two law enforcement officials identified the driver as 34-year-old Miriam Carey, of Stamford, Conn. She was traveling with a 1-year-old girl who avoided serious injury and was taken into protective custody.
The officials spoke on condition of anonymity because they were not authorized to discuss an ongoing investigation.
Carey's mother, Idella Carey, told ABC News Thursday night that her daughter began suffering from post-partum depression after giving birth to her daughter, Erica, last August.
"A few months later, she got sick," she said. "She was depressed. ... She was hospitalized."
Idella Carey said her daughter had "no history of violence" and she didn't know why she was in Washington on Thursday. She said she thought Carey was taking Erica to a doctor's appointment in Connecticut.
ABC News reported that Miriam Carey was a dental hygienist. Her boss, Dr. Steven Oken, described Carey 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."