Every Mother’s Day, Pei Xia Chen gets a present from her late NYPD detective husband Wenjian Liu: their daughter Angelina.  The effervescent eight-year-old was born via artificial insemination about two and a half years after her father was murdered – using sperm harvested on his deathbed. “She’s truly my miracle baby,” Chen, 44, told The Post. Pei Xia Chen said her daughter Angelina is her “miracle baby.” J.C. Rice for NY Post “What makes it even more special is how much she reminds me of her father, Wenjian. Every time I look at her, I see a part of him still living on through her,” the widow said.  Liu, 32, and his partner Detective Rafael Ramos, 40, were murdered while on patrol on Dec. 20, 2014 by cop-hating career criminal Ismaaiyl Abdullah Brinsley, who gunned down the pair as they sat in a marked squad car in Bedford-Stuyvesant. Brinsley — who was wanted in Baltimore for shooting his ex-girlfriend in the stomach earlier that day — then fatally shot himself in the head.…