A court document says the 12-year-old girl stabbed 19 times in some woods in Waukesha narrowly escaped death.
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.
According to a criminal complaint, the girls said they had been planning to kill their 12-year-old friend for months to please Slenderman, a fictional online character.
The complaint said they invited the girl to a sleepover Friday. They planned to tape her mouth shut, stab her in the neck and run away to Slenderman's mansion.
Instead, they attacked the girl in Waukesha on Saturday, handing the knife back and forth between them before one girl held the victim down and the other stabbed her 19 times.
One girl told detectives she regretted it. The other said she was sorry.
The Associated Press contributed to this report