Hi J., I was actually in 3 tornadoes as a child. The first one I was about your daughter's age, and I was in a car with my older sister. The second one I was in a cellar at age 11, and the third one I was at Valleyfair laying in a ditch on the other side of the old wooden roller coaster (age 17). Needless to say, I had a lot of fears. I won't say I've overcome them completely, it took a long time, but I can share a couple things that helped me.
First, if you are a spiritual person, prayer helps tremendously, especially when people would pray for me in person. My own prayer life helps as well.
Second, she needs to know that Mom understands and respects the storms. That means you need to keep a close eye on the weather, and when severe weather is approaching, take all necessary precautions. Help her learn about the weather and how storms develop, learn about the different cloud formations, etc. I had a dad who was a weatherman, so I was lucky there, but you can get books from the library. Our local TV station does a great weather presentations at elementary schools, where the kids get to meet the weatherman. You might check into that. Education is power.
Third, I agree with others who said to go help clean up. Nothing is better to take the focus off yourself.
You're welcome to email me if you want to talk more. ____@____.com