Updated Saturday morning.
Sara Kelly, 20, was arrested and charged with her murder, police say, adding the two "were known to each other."
The Herald reports another woman was taken into custody and that the victim leaves five children. Friends of her children identified her as Shannon McCormick.
McCormick is South Boston's fourth murder victim this year. On May 27, two people were stabbed to death and their Linsky Barry Court apartment set on fire. On April 16, a woman was stabbed to death on E. 7 St.