Book: 'Mother Teresa: Come Be My Light'

I read the book "Mother Teresa: Come Be My Light", which is a collection of her letters written to her superiors during her work in India. Since I have not seen the movie, I assume this book inspired "The Letters" and I am wondering if it's possible at all for a movie to indicate so much inner struggle.

The results of her work and the immense good she did cannot be refuted. The fact that she was plagued by darkness and doubts makes her sacrifice even more admirable. She was an inspirational, intriguing character and I am really looking forward to seeing the movie!