Hey there,
I wanted to answer this when I first saw it but was out of town...I love dreams!
Anyway, I wanted to come by to put your mind at ease

. Death in a dream certainly most often signifies the "end" of something, but it does not necessarily mean the end in a negative way - for example, it could mean that she is "finished" with some issue at hand.
And like the other posts, it may have just been something triggered by television or school, that has nothing to do with you or family at all. It could have even been something she ate before bed, and you happened to be the last one she saw before falling asleep.
At any rate, when she next tells you a dream she had, you might think to ask your DD how it made her feel and what she "thinks" it might mean. How she explains how she felt about it might clue you into what's on her mind (if the dream is coming from something that is bugging her). Since it's your DD's dream, and symbolism is very personal, she's actually the best one to analyze it!
It's great that she was able to remember her dream vividly, and that she came to tell you about it. So don't you worry about the death part. There's nothing scary in there at all. If she has recurring nightmares about it, you might suggest to her that she always has the option to "change" the dream into a happy or funny dream. Suggest, for example, that if in her dream she sees you die, that she should then realize that you are stifling your giggles, and then to make you pounce up and say, "tada!" And have a nice laugh about it.
This is called Lucid Dreaming, where you become aware that you are dreaming while you are dreaming, and then you have the ability to control your dream. I know it sounds a bit out there (or even way out there for some LOL), but it's actually an incredible way to learn a lot about yourself...and have a really, really fun time, too (think flying whenever you want to, or swimming in the ocean while breathing). It's a wonderful tool to help yourself see the positive and grow, and also to face and overcome your feelings of fear, and should be a real cinch, especially at 12 years old.