Police discovered the body of a 4-year-old girl weighing only 15 pounds this morning in Brooklyn. Apparently Marchella Pierce's arms and legs were tied to her crib with twine and a jump rope; cops are questioning the mother, 30-year-old Carlola Pierce, who said she found Marchella's lifeless, severely malnourished body in the family's Bushwick residence at 4 a.m., but waited three-and-a-half hours to call police. According to the Post's sources, the living area of the house was filthy and Marchella had trauma to her arms, ankles and wrists, and appeared to be underdeveloped with undeveloped lungs. There was also an oxygen tank next to her bed, which she wasn't connected to. Girls at age 4 have a median weight of around 35 pounds; 15 pounds is the median weight of a 6-month-old girl.