how often does she have these visions?
I would say that she has seen something scary on TV or the computer, or someone has told her something really scary ,has a member of the family been chatting to her more , is she looked after by anyone else other than you . Sometimes school friends may also pass on scary happenings All you can do is reasure her , that you are okay , and not make a big deal of it as it will feed on itself and create anxiety Good Luck.