Personally, I think it depends on how much you want to tell her.

My DD is a sensitive soul when it comes to illness and death - she take great interest in it and wants to know as much as possible. I try not to sugar coat things but I am selective in what I tell her. When the subject of death has come up and she's worried about her own mortality or that of myself (she never seems worried about Daddy), I tell her that mostly people who die are either very sick or very old. We don't know anyone who has died in a car accident or other traumatic and unexpected circumstances, so I haven't mentioned that to her. DD seemed to accept my explanation and it settled her mind. I don't doubt it is a conversation that we will revisit many times. But for now, I tell her that those who are unfortunate enough to pass are very sick or very old. And she is neither of those things. I once tried to tell her I'm neither of those things but she insisted I WAS very old...