My DD who is about the same age started this too. She would come downstairs from bed sobbing. Sobbing saying she doesn't want to die.
It didn't seem an immediate thing - more a long term fear.
This happened a for about a week. Waking in the night crying, randomly saying she had intrusive thoughts while eating her dinner.
I spoke to a teacher at school who sent home a book to read together about dying. It DID NOT HELP. She cried from page two and for half an hour afterwards. Sobbing.
I said she should think of happy things to block out the bad thoughts but we know that's easier to say than do.
I decided it must be something to do with the events in Paris. Although she has no internet access and does not watch any adult TV - still they had an assembly at school with two minute's silence. Plus she hears the radio news in the car which is designed for adult's ears.
A breakthrough came when we were listening to the radio and they started talking about Paris - she covered her ears completely. I said listen to this and she refused. But I said listen - the news is telling us they have found the bad men and shot them. They are all dead.
DD looked visibly relieved!
Since then she has been less fretful and hasn't come down from bed crying since.
Sorry long post but it does match up with the timings you mention and sounds exactly the same. Maybe you can subtly mention Paris and work out if it is related. Maybe again see if you can get her to overhear how the bad people have been caught and stopped.
Good luck - it's heartbreaking isn't it.