I hated the Shack. I think I'm in the small minority on that one, but I really did.
I would heartily second Lysa TerKeurst, especially her book Unglued. It's awesome. She has a brand new book, The Best Yes, but I haven't read it yet. (It's on my Christmas list!) I LOVE her. She's someone you want to hang out with, she's flawed, she's real, and she loves Jesus.
Another fantastic book is A Confident Heart by Renee Swope.
If she wants to study the Bible, I would really, really recommend Rick Warren's Bible Study Methods. I seriously learned SO much about how to sit down and study the Bible. He has some wonderful ideas on how to get more out of the scriptures you read. My favorite is to go through a verse once for every word in the verse and emphasize each word, so you can think on the significance of that particular word, even words we think of as filler, like a, the, an... We did an entire 8-week Bible study on the methods in the first chapter alone.