Which ones of the many books written about Mother Theresa's? The one I have is Come be My Light and, a few articles on her journals. The best one of the latter is Sacred Doubt written by Rabbi Irwin Kula of Yearnings: Embracing the Sacred Messiness of Life
http://newsweek.washingtonpost.com/onfaith/irwin_kula/2007/09/sacred_doubt.html

The feeling of being unaccompanied by God was not exclusive to Mother Theresa though. Many saints have gone through the same. St Augustine and St Theresa of Liseux as well, to name a few. St Faustina of the Divine Mercy movement wrote extensively about it: Dark Night of the Soul. Here's an extract from it from my Catholic book club:

"Toward the first year of my novitiate, darkness began to cast its shadow over my soul. I felt no consolation in prayer; I had to make a great effort to meditate, fear began to sweep over me. Going deeper into myself I could find nothing but great misery. I could also clearly see the great holiness of God. I did not dare to raise my eyes to Him, but reduced myself to dust under His feet and begged for mercy. My soul was in this state for almost six months...

Further on, she continues with:

"My mind became dimmed in a strange way no truth seemed clear to me. When people spoke to me about God, my heart was like a rock. I could not draw from it a single sentiment of love for Him. When I tried, by an act of the will, to remain close to Him, I experienced great torments, and it seemed to me that I was only provoking God to an even greater anger. I felt in my soul a great void , and there was nothing with which I could fill it. I began to suffer from a great hunger and yearning for God, but I saw my utter powerlessness. I tried to read slowly, sentence by sentence, and to meditate in this way, but this also was of no avail..."

P.S. St Therese of Avila not Liseux.