Carine McCandless asked Krakauer to leave out the severe physical and emotional abuse she and Chris suffered at the hands of their parents. It's there if you read between the lines, or recognize signs of unresolved childhood trauma, in both the book and movie. He basically left out the whole "WHY?" part of the story, just explaining what Chris did and when. Carine only allowed a small, negligible reference in the movie when Chris reads a poem to her about a toxic married couple and when movie-Carrine asks who wrote it, Chris said it could have easily been either of the two of them.
After both parents died, Carrine published a book called The Wild Truth {Goodreads Amazon}that explained the abuse and why she had asked Krakauer to leave it out. Krakauer wrote her book's forward, giving his perspective of what was in the book & movie and what was left out and why. Long story short, she wanted to wait until their parents died to tell the whole truth to preserve an already delicate family relations. The book isn't wonderfully written, but it's a good companion piece to the book and movie because it finally explains why he ran away so recklessly.
The Wild Truth it explains a lot and she's had an interesting life in her own right