A mother of three young children was fatally shot when she stopped by a makeshift shrine for a rapper who was killed last week. Police say 27-year-old Nancy Williams was hit by apparently random gunfire behind the Stuyvesant Garden Houses on Gates Avenue. Fans of rapper Leval Lyde had gathered to remember him a week four days after he was gunned down on Clinton and Fulton Avenues. A cop explained to the Post, "They were......