My Sister's Keeper

I have read the book, written by Jodie Picoultonce. Guess, that's years ago. But I still remeber the story and especially the surprising end.
Here is a short overview:
My Sister's Keeper is a fictional novel written by Jodi Picoult. The story follows the life of 13- year-old Anna Fitzgerald, who enlists the help of an attorney, Campbell Alexander, to sue her parents for rights to her own body. Kate, Anna's older sister, suffers from leukemia, and their parents conceived Anna through in vitro fertilisation to be a genetic match donor for her sister Kate. Anna donated genetic material throughout her life, such as blood and bone marrow. Now, their parents want Anna to donate a kidney to Kate, but Anna instead files a lawsuit against her parents for medical emancipation so she will not be forced to donate one of her kidneys to her sister.

When getting to know that there will be a movie I had conflicting views. First, only a couple of movies are as good as the books they are based on.
But then I saw the trailer and did read some good reviews.
Well, even knowing that I probably would regret it, I went to see the movie:

I was astonished! What a great production. A relator is to hear in the very beginning. That was annoying but worked out well. Cameron Diaz and Alec Baldwin and to their site Abigail Breslin as Anna and Sofia Vassilieva as Kate. I liked the movie till 10 minutes before the end.
Of course there were enough women watching the film who started to cry. Sniffing, snuffling and sobbing all around me.

But then! Why can't they stick to the book till the very end? Why the hell did they change the end?
Kate dies, Anna survives and the family remembers Kate life by spending the holidays in Montana. F...

This could have been a superb movie - it is 'just' a good one.

What is quite unbelievable to me - Jodie Picoult is Co-author...