I looked up the book and got this description from Feinberg's website:
"The Organic God
Natural. Pure. Essential.
In our ever-changing world, simplicity is a craving. What if we could simplify our lives starting with our faith? Imagine what it would look like to have an organic relationship with God, one that is stripped of all pollutants, additives, and other distractions that can cloud this ultimate relationship. The Organic God removes the unhealthy fillers and purifies our relationship with the God of the Scriptures."
So it would appear the idea is not that God is somehow "organic" as HeartSong has defined but rather in terms of organic agriculture -- that is, pure and untainted by man's devices.
Anyways, I personally wouldn't read this book or recommend it. And if I were to judge this book by its cover, I would say it seems similar to a Joel Osteen book aimed at the Christian bookstore market for women.
Perhaps it might help to encourage your sister-in-law to read Ecclesiastes. It is one of those awesome motivational and life-focusing books of the Bible. No, really, it is.