The book wasn't about Islam. It also wasn't about Christianity. It was about the Dominion Theorcracy which resembles more what we see with the religious extremists in America.

Edit: I would like to add that it also fits religious extremism in Islamic countries, but that's not what the aim of the author was. She definitely meant America and their extremists. She even created a flag that looks awfully similar to the American flag.

Dominion Theology is a group of Christian political ideologies that seek to institute a nation governed by Christians based on their personal understandings of biblical law. Extents of rule and ways of achieving governing authority are varied. For example, Dominion Theology can include theonomy, but does not necessarily involve advocating Mosaic law as the basis of government. The label is applied primarily toward groups of Christians in the United States.