She went into the restaurant to feed the infant, witnesses said, and the baby stopped breathing shortly after that.
It was not immediately known whether the girl had an existing medical condition that might have contributed to her death. The exact cause and manner of her death will be determined by the medical examiner or the baby's doctor, police said.
Protesters gathered in Baltimore for a second day Saturday in protest of a police shooting on Friday.
Authorities opened fire on a knife-wielding man after they were told he was threatening people and armed with two knives. He ignored police commands to drop his weapons, Baltimore city police Commissioner Kevin Davis said at a news conference Friday, and a stun gun failed to take the man down.
"He's threatening people waiting at the bus stop," Davis said, praising the citizen who called in the incident. "And I'm so proud of these officers, the way they responded to the scene, the way they attempted to de-escalate. Unfortunately, that didn't work."
Two officers, identified as Officer Gary Brown, a 16-year veteran of BPD, and Officer Supreme Jones, who has been with the department since 2014, opened fire on the man, the Baltimore Sun reported.
He was transported to the hospital in critical condition.
Police said one of the officers was wearing a body camera.
The shooting took place just days after officers opened fire on a man armed with a handgun, authorities said.
An officer stopped a station wagon around 10:40 p.m. Tuesday after noticing the vehicle's obscured tags, according to police. The officer, identified as 24-year-old Officer Jeffrey Melo, called for backup.
The officers flanked the vehicle on either side, with Melo taking the driver's side, police said. The officer on the passenger's side of the car spotted a gun on the man in the car, identified as 29-year-old Richard Allen Gibbs, and shouted a warning to Melo.
Melo fired one shot at Gibbs, hitting him in the shoulder. Gibbs was taken to the hospital in critical condition. He was expected to survive.