Let me start by saying that I am hugely supportive of therapists, friends, and family members recommending medical, scientific, or fact-based books on mental illness to those suffering from it. I'm quick to do so myself. There are a lot of great "this is what depression is" books out there that can provide a foundation for understanding your own issues or those of a loved one. But I don't know that I'd consider a therapist recommending Co-Dependent No More or Listening to Prozac to be bibliotherapy any more than I'd consider a doctor recommending a book about living sugar-free to a diabetic to be bibliotherapy. So we'll take those recommendations out of our discussion.
That leaves us with a few other options for bibliotherapists to recommend: experiential memoirs and novels. I think you could also make a case for poetry as a third category, but I think most poetry can either fit pretty broadly into the fictional category or the memoir category. Another way of categorizing books that help a person cope with either a significant life event or a mental illness would be books that help you process your own experience and books that provide an escape.
What I would argue in terms of bibliotherapy for both types of books is that one size does not fit all. I'm going to use Hyperbole and a Half as an example in terms of experiential memoirs. I love the site and the book and I recommend it all the time. But despite the fact that the author struggles with depression and I have struggled with depression, I don't identify that closely with her experience. I appreciate her experience, but I don't read it and think "That's me!"
The problem is even more difficult in terms of novels. Yes, a person can do a Google search for novels about depression and recommend the top results to a person struggling with depression, but my own personal experience has been that finding the right book at the right time is much more organic than an Amazon algorithm. If I were to name the novels that have meant something to me during times of depression, even novels that I feel like were life-changing in terms of helping me cope, I wouldn't name a single novel that is specifically about depression. All of the books that have touched me in the right place at the right moment have been serendipitous choices that I don't think could be prescribed like a medication.
Obviously, bibliotherapy isn't something I've tried. I have read some of the literature that is promoted to librarians interested in the topic by the ALA (The Helping Troubled Teens series). I'd be interested to hear other people's opinions on bibliotherapy, of course. Do you think this is a viable form of treatment? Who would you trust to provide bibliotherapy?