I don't know if this is of any help to you, I just wanted to share my story. When I was 6 years old, I watched the movie "La Bamba", and became terrified of airplanes and helicopters. It was even to the point that if I would see or hear an airplane, I would run inside, or underneath a porch, thinking I was safer there. Even if i was in bed, and heard a police helicopter, I would cover my ears until it went away. And this was all due to a stupid movie. This fear, although it isn't nearly as bad, stayed with me most of my life. Growing up I would always dream of planes crashing on me, etc. As a teenager, I grew out of the "running inside" or "covering my ears" stage, thank God! LOL! But I was still terrifed to fly or even be near a low-flying plane. And i would still have the occassional dream. Then, once I was 20, I had mostly out-grown that irrational fear all together, and even considered flying, which I still had never done. Last year, at 23, I flew for the first time. And I was scared to death! But I did it, and I didn't like it, but I would do it again if it was to go back to the Caribbean! Anyways, sometimes kids get terrified even if something didn't happen to them. Maybe it was just something they saw in a movie, or something they heard about. And it will stay in their brain unless someone helps them get through it. That was my problem, I never told my parents because I was embarassed! Good luck to you!
When fears develop in young children, they are most often irrational and unexplainable - i.e., they do not stem from unfortunate experiences and it is not possible to discern the origin of the fear(s). That seems to be the case with your daughter. Now, some children are fearful by temperamnet - they are easily upset and anxious about any number of things. Other children experience more circumscribed fears (e.g., of clowns, of loud noises). There is no telling how your daughter will develop - time of course will tell. But it is important to be patient, supportive and reassuring, without keeping her from experiences that are normal for a child her age. Generally, as children grow and develop and have more experiences 'under their belt', so to speak, reality testing allows them to relax about some things they formerly feared.