An illustration of Gertrude Bell's continuing influence on policy can be found here.

The best account of Bell's impact upon the international relations of the Middle East is:
Liora Lukitz, A Quest in the Middle East: Gertrude Bell and the Making of Modern Iraq.  I.B.Tauris, 2006. (ISBN 1850434158, 9781850434153)

More detail about her social context and  British government circles is found in Janet Wallach, Desert Queen: The Extraordinary Life of Gertrude Bell: Ad-venturer, Adviser to Kings, Ally of Lawrence of Arabia . Doubleday, 1995.

Bell herself wrote many books and articles, enumerated here.