In my dream my sister had come from her school ski trip in Lake Tahoe Californa. When I asked her how her trip was she told me it was a horryifying disaster. When I asked her why she told me that several of her classmates had suffered serious injuries and that one girl had died. I asked who the girl was and she told me her name and I can not seem to get the girl's name out of my head. All I remember thinking about was my sister and her classmates talking to the police about this horrific tradedy. Then I woke up. What does this mean?

I think (and it has been just my thought over the years-I have zero expertise but have drempt about deaths of family members myself several times over many years) that the mind prepares itself to handle the concept of death, which everyone will surely experience either personally or through loss of loved ones.
In my case, it was never a premonition for the near future.
The mind and body (in my humble opinion) are primarily 'wired" for survival instincts.
Dreaming of death may be the brain's way of helping us accept the concept of death, and preparing us to "survive" the experience of especially the death of loved ones.
A very lame example: Caveman's mate dreams of her provider's death which causes her to wonder what will become of her and the family if the providers is crushed under a wooly mammoth's huge foot. Maybe she decides to learn more about gathering food and protecting the cave because of the dream, which increases her eventual chances of survival.
I said it was lame.
On the other hand, sometimes my dreams have been very specific about things that are on my mind. It could be that the brain is trying to tell us to take some action to prevent what we are concerned about from happening.
These opinions are based on my own experiences and thoughts and not much else.