I don't know about books regarding dealing with fear. Which, by the way, all equestriennes do. But a really nice book about riding in general is one called, "Centered Riding" by Sally Swift. It uses a lot of imagery to help you think about riding in other terms. Some people find this helpful, some do not. But, when one is afraid, I think it can be very helpful to have an interesting image or goal to focus on. Takes one's mind off of thinking about what might happen and brings one back into the immediate present , to thinking about such things as riding with "soft eyes" , or letting your legs reach down like the roots of a tree.
Check it out.