I have never lost a child but I have lost someone to suicide.
Unfortunately all you can do is be there when she needs you. Losing somebody to suicide is very different to losing them to say a car accident or illness. So many emotions go through your head, hate, guilt, frustration just to name a few. The main one people go through is the guilt of not being able to stop it, a part of you hates yourself for not being able to stop them from taking their life.
I also understand her cutting people out of her life if they refuse to talk about him, he was a massive part of her life and to act like he didn't exist hurts. I started recently cutting out people that tell me its time to get over what happened, it is something you can never get over.
I would suggest asking her to see a suicide support group if there is one in her area, best thing I have done because the ladies are wonderful and supportive and you can talk about your loved one without judgment. You get to talk to people who understand all the crazy feelings you have.
If she is on facebook there are plenty of pages with support on there.
I have found this one to be really helpful: http://www.facebook.com/pages/Survivors-of-Suicide-Bereavement-Support-Association-Inc-SOSBSA/164602631156?ref=ts&fref=ts