Orson Scott Card, maybe? A lot of his sci-fi and fantasy stuff touches on religious themes. He’s also got a couple of interesting books about Old Testament characters – the best of these is Sarah.
Odd that your spellchecker picked that up at all, given that “fiends” is a word. I think you mean “proofread” 
To answer the OP, you asked for “faith-related” but you didn’t specify if it had to be Christian faith-related. I kinda got the impression it did, but if not, The Satanic Verses is an excellent (if long) read which approaches faith from a dozen different directions.
(it’s sorta about the revelation of the Qu’ran, in case you were wondering)
John Irving’s A Prayer for Owen Meany is one of the best books about faith I’ve ever read, and it’s done in a completely non-religious way.
I’d also recommend The Autobiography of Malcolm X* for a look at the transformative nature of finding faith.
You are so looking for Walker Percy’s The Moviegoer and Douglas Coupland’s Life After God. Both are very, very secular explorations of near-deafening, Kierkegaardian forays into faith. Brilliant.
Brighton Rock, also by Greene, is another book to consider. It contains of of my favorite quotes:
I would suggest just about any book by Madeleine L’Engle. One of my all time favorite books is A Wrinkle In Time .
Also, my book group just read Life of Pi by Yann Martel. Very allegorical, a lot of religious elements in it.
Right. I was supposed to read The Moviegoer a while ago. I should see if it’s in print.
Second vote for A Canticle For Leibowitz. It’s very good.
The book group at my church read that one. We had a great time discussing it.
We also read Peace Like A River by Leif Enger and The Secret Life of Bees by Sue Monk Kidd. Both were very good books.
THE KINGDOM OF THE WICKED, which is kinda his novelization of his screenplay for the NBC miniseries A.D., kinda a sequel to JESUS OF NAZARETH, for which he also wrote the screenplay & inspired his novel MAN OF NAZARETH.
Btw, Burgess also hoped to do the screenplay for a Conversion of Constantine miniseries to complete a trilogy- no idea if he actually did any work on it.
A second vote for Ann Tyler, Saint Maybe.
Dorothy Sayers’ mystery novels also frequently had elements of faith and conscience, and are very well written.
I second Walker Percy- he was a great Southern Gothic Catholic social satirist-
(tho THE MOVIEGOER is the one novel of his I have not read-)
I have read-
THE LAST GENTLEMAN, which I didn’t care for & don’t recall much of;
it’s sequel THE SECOND COMING about a middle-aged man whose chemical imbalance leads to an obsession about the title subject & how his quest leads him into the arms of a young emotionally-withdrawn woman (I liked it much better)
LANCELOT- a man confesses to his best friend, now a psychiatrist/priest, of how he sought to confirm God’s existence by committing real sin- also rrecommended
LOVE IN THE RUINS- my personal favorite, subtitle The Adventures of a Bad Catholic at a Time Near the End of the World, brilliant but somewhat dated (& occasionally prophetic) social satire of early 70s political & religious division
THE THANATOS SYNDROME- LitR’s decent but lesser sequel. Deals with lots of life-termination & mind manipulation issues.
LOST IN THE COSMOS- The Last Self-Help Book- humorous philosphical-theological-sci-fi observation of life
Two books of essays- THE MESSAGE IN THE BOTTLE and SIGNPOSTS IN A STRANGE LAND- pretty good but not what I would start with.
I’d start with 2nd Coming, Love/Ruins & Lancelot.
More recommendations-
C.S. Lewis- TILL WE HAVE FACES a dark challenging retelling of the Eros & Psyche myth, not as overtly Christian as most of his fiction (Btw, tho I’ve heard other make the same comment of THAT HIDEOUS STRENGTH that Shodan has, I have the opposite view. THS is the best of the three IMO.)
Also by Lewis- THE GREAT DIVORCE- a Journey into the Afterlife
Various novels by Father Andrew Greeley, mystery/romances- usually based around a screwed-up Irish Catholic man & a screwed-up Irish Catholic woman thrown together by a screwed-up Irish Catholic God.
DEAR AND GLORIOUS PHYSICIAN by Taylor Caldwell- The Greek physician Luke wages war against an uncaring God by helping the victims of His negligence, then he meets some who claim He has become a man… Kinda overwrought but I like it.
Jame BeauSeigneur THE CHRIST CLONE TRILOGY- In His Image, Birth of an Age, Acts of God- an truly literate exciting & intriguing End Times saga, would be the best selling series rather than LEFT BEHIND if the mass reading public had any taste.
Aldous Huxley BRAVE NEW WORLD
Jan Karon’s MITFORD novels- Old Episcopal priest Father Tim & his new wife deal with tragedies & challenges & friendship & happiness in a small Southern town.
Others have recommended various works of science fiction and/or fantasy, but here’s an online list: http://www.spectacle.org/396/scifi/pavlac2.html
You may want to look at a short story collection by Flannery O’Connor. All of her short stories deals with faith in one form or another.
Do they have a sense of humor? Lamb
C.S. Lewis’ The Screwtape Letters. Great, humorous view on the trials and temptations of the Christian life from the “other side”. And, if she doesn’t mind slightly more Christian-type writing, the “Narnia” series.
Ray Bradbury’s Martian Chronicles has a number of Christian-type stories.
And what’s wrong with reading the Bible? Sure, some of those genealogies might run a little dry, but the narrative portions are pretty exciting. And some people consider that to be fiction, too, but let’s not go there. 
Thanks for all the suggestions. There are some very good ones here. I’ll run them by her and see what she thinks.
They may also enjoy the trillogy from Marjorie Holmes on the life of Christ.
Two from Galilee Mary and Joseph’s story
Three from Galilee The begining of Jesus’ ministry
The Messiah the final days of Jesus’ ministry, death and resurrection.
Or The Red Tent by Anita Diamant
The Women of Genesis books by Orson Scott Card are good as are the Lineage of Grace series by Francine Rivers.
I also love Skeleton in God’s Closet and More than a Skeleton by Paul Maier. Great gripping reads.