Doctors at Waukesha Memorial Hospital told police the girl was "one millimeter away from certain death" because one of her stab wounds missed a major artery near her heart by a millimeter.
The document says a surgical team performing laparoscopic surgery on the girl found injuries to her liver, pancreas and stomach.
The hospital declined to update the girl's condition Tuesday. Police said Monday the girl's condition was stable.
Two of the victim's friends, both 12, are charged in adult court with first-degree attempted homicide. They are each being held on $500,000 cash.