I wish you had access to a therapist who could do play therapy with your daughter, because that would most likely help her. When my daughter (now 30) was 3 years old she developed a terror of fire. Like you, my husband and I could not come up with any reasons for my daughter's terrible fear. She would completely panic when we took her places because she was so afraid the place would catch fire. We took her to a play therapist, and kept her in therapy throughout her childhood. The therapy helped her immensely. Even now she uses "tools" she learned as a child from therapy.

I feel so sorry for your daughter. As an adult fears are horrible, but as a little child, with the world so big and mysterious, it must be absolutely terrifying to be victimized by such fear.