I feel so sad upon knowing the death of someone I know...

I find it kind of strange you feel sad about this. You were no close friends at all, just met once in a while on facebook. So is this about feeling quilty or because of her age? And what has age to do with it at all? From the moment on you are born you are dying. If you like it or not. Nobody has the guarantee he/she will get old. This is just a fixed idea we all have in our head. For some reason it must be great to get old. But most old people are pushed away being useless for the society (no job, only consuming, not taken serious by their life experiences, always sick, just consuming, too slow, too smelly, living from old memories, always repeating themselves, etc etc). Might be she left soon to your opinion but what is soon? There are 15 year old children/people who have 100 times more life experiences as 80 year old people. I believe her work here is finished. There is no need to stay longer, to learn more. She is finished here and it's good the way it is. Sorry but it does sound weird to me that people you never meet or met in real life feel sorry or sad or grieve if you die. So many do say that also about people (children included) who live alone or a lonesome life and still would be if they were still alive.

Only God who knows why? All of human being must die,that was our destiny,no one forever,now what you gonna do is just try to be nice person,help each other and enjoy your life.I am so sorry for your friend story.

this is so sad. having a friend you know for a long time and for just a span of days then you will knew that she had left the earth is so tragic. Just pray for her soul and to have peace in the other life.

Even if we don't want it to happen, this is life. I have best wishes for her family and loved ones, it hurts to lose a loved one.