Angelina was born Tuesday to Pei Xia "Sanny" Liu at Weill Cornell Hospital in New York City, the NYPD said in a blog post.
Sanny's husband, Detective First Grade Wenjian Liu, was shot and killed on December 20, 2014. The night of the incident, Sanny requested that her husband's sperm be preserved.
The slain officer's parents, Wei Tang Liu and Xiu Yan Liu, were there for the birth, according to the NYPD.
Sanny became pregnant through a process called in-vitro fertilization. In-vitro fertilization is when a sperm and eggs are removed from each parent and mixed together outside of the woman's body in a laboratory to create an embryo.
"I told my friend, 'It's going to be a baby girl,'" the new mom told the NYPD. "My friend said, 'No, you haven't even checked the sonograms,' but I was right."
The couple had been married only a few months at the time of his death. The two had always dreamed of having a child together.
Liu and fellow police officer Rafael Ramos were killed while working in a "critical response" detail in an area with higher crime, according to police. The two normally worked in downtown Brooklyn, but that evening, they were assigned to work elsewhere.
The gunman approached the passenger side of the car and took a shooting stance. He opened fire and shot both officers in the head, then-NYPD police Commissioner William Bratton said at a news conference.
They were "shot and killed with no warning, no provocation," Bratton said. "They were, quite simply, assassinated."
CNN reached out to the Detectives' Endowment Association, which is handling media requests for the family, but had not received a response Wednesday.