A SCHOOLGIRL stabbed a woman 143 times then left her body in a burnt-out home for police to find in a pre-meditated murder, a court heard. Marta Bednarczyk, 43, was discovered at the terraced home in Wellingborough, Northamptonshire, in March. Jurors heard a 13-year-old girl, who can’t be named, initially claimed a third party had…