Sheri Williams was standing in the doorway of her Birmingham apartment holding her 10-day-old son when she was hit, al.com reported Monday.
Her son was not injured, police said.
A man chasing another man down the street fired the shot, a police spokesman said. The two men had been in a fight at a nearby restaurant.
Williams was hit in the chest and fell onto a couch, the spokesman said. She was found dead when authorities arrived at the scene.