Hi,
That is a truly upsetting dream. Dreams like that are always upsetting. However, if it makes you feel any better, dreams are often symbolic rather than literal. Also, dreams are often reflections of anxieties and not indicators of possible realities. Do you have any anxieties regarding your daughter's health? Is there anything going on - not necessarily heath related - that concerns you regarding your daughter? How old is your daughter?
On a symbolic level, what was the context of the dream? Did your daughter just appear and tell you this or were there other things going on in the dream? What was your response in the dream? Why was your daughter telling you this? And finally, and I know this sounds like a stupid question, but what was your reaction in the dream? Were you frightened, calm, resigned, etc.? And what was your daughter's emotional state in the dream?
Finally, one thing to consider is that dream characters can also actually be symbolic of our selves. That means that your daughter might not literally be your daughter, but rather some aspect of you. And if that is the case, then the death would not be a literal death, but an integration of or a maturation of some part of yourself, which to the un-integrated part might feel like death - that's why the emotional content that you felt in the dream itself is so important.
Let me know how you're doing!