The five stages of grief are:
Denial
Anger
Bargaining
Depression
Acceptance
http://en.wikipedia.org/wiki/K%C3%BCbler-Ross_model
Sometimes, people bounce back and forth from one stage to another, such as bargaining with God first and then anger. Your friend is going through the anger stage of grief right now.
If you contact The Compassionate Friends (see link below), they may have a chapter in your area or be able to suggest a group your friend could attend.
http://www.compassionatefriends.org/home.aspx
Some people do not like to participate in grief support groups for privacy reasons or because they feel that no one can possibly understand what they are going through. That is so wrong because a person who has had the same experience is the only one who can understand.
I reluctantly attended a grief support group over thirty years ago, and it was a great help.
For parents who have lost an older child and the parents friends, I recommend The Bereaved Parent by Harriet Sarnoff Schiff.
http://www.amazon.com/BEREAVED-PARENT-Harriet-Sarnoff-Schiff/dp/B001AE4O8E/ref=sr_1_1?s=books&ie=UTF8&qid=1325384489&sr=1-1
From the comments on Amazon:
This is the book I recommend first for bereaved parents, and for those who, powerless in observing such pain, want to understand.
It is normal for your friend to be angry, but she should seek counseling if she becomes stuck in any one of the grief stages.
You are a good friend to try to help your friend cope; many people avoid grieving parents. It can be a very lonely place.