C.L.
Just to let you know you are not alone we went through the same thing at that age. It did last for a couple of years, but not at the same intensity. Like some of the other responders said I think it is most helpful to acknowledge her fears without overreacting and to educate her. Our son is now 12 and although he no longers panics with severe weather he has an odd fascination with it and some of his favorite reading material is a book about tornadoes. He is good at math and science so I tell him he should be a metereologist!