The death of an adult child, in my opinion, is one of the hardest losses there is. It is all so wrong. My youngest child, died aged 25 years of age as the result of a tragic accident. We had no chance to prepare in any way and I can still remember saying to the policeman who came round to inform us that he can't be dead as I do not have any funeral arrangements for my children!!!!
He should have been celebrating his 44th birthday today - and despite how long ago it was, I still get tearful when I think of him. A gap in our family that can never be filled!!! Despite five other children and eight g.children.
When he died, all I wanted to do was to talk about him, on and on, endlessly. I can remember just over a week after his death someone telephoning me to say that a meeting I had been due to attend, which had been delayed due to this, was now going ahead and they all hoped I would be there, I told the caller that I was not sure about attending as I was now the worlds greatest bore, as all I wished to do was to talk about him. After a very slight pause, she said 'Come along and bore us'. One of the nicest thing anyone has ever said!!!
So, my advice is to let you friend talk to you, by phone, by email, by skype, however.....about her daughter as often and whenever as she wishes. Be there, and be willing to listen to some stories over and over again. And be aware that this need may go on for a very long time.
It will take a very long time for the very sharpest mourning will start to disperse - took me a good two years. For many people, they are very good at sympathy and support for a few weeks, but then they get on with their own lives (understandably), - for the parent, it will continue. So, the fact that you are not with her in these early days and weeks can be made up for over the next months and years.