Everything is looking pretty good in the final chapters of My Sister's Keeper. Anna reveals that Kate doesn't want her kidney and this whole trial was her idea, meaning that it's okay for Anna to keep her kidney and for Kate to die, so that Anna doesn't seem like a villain. Taking this into consideration, the judge grants Anna medical emancipation from her parents and awards power of attorney to Campbell, who feels like he's built a little surrogate family: "I will have Julia, and I will have Anna" (10.6.19). Yay.
Then… well, the unthinkable happens (especially if you're seen the movie, which has a different ending): Anna and Campbell get in a car accident right after the trial, and Anna is killed. Since Campbell has power of attorney over Anna, he tells them to donate her kidney to Kate. Anna dies, Kate lives, and nothing is as it was intended to be.
Later, in the epilogue, Julia and Campbell get married, Jesse becomes a cop, and Brian and Sara feel guilty for pretty much neglecting Anna for thirteen years (as well they should). So, in short, it's a happy-ish ending that's decidedly unhappy when it comes to Anna.
Did you see that car crash coming? (If Campbell did, Anna might still be alive…) Do you think the ending is about how random things can change, or end, our lives forever? When you think about it, a car accident isn't any more or less random than Kate's leukemia, right? Judge DeSalvo is done, Shmoopers, so you be the judge.