Book Publishing Legal Issue - Defamation of Character?

I run a publishing company and have an author who would like to publish an autobiography. The book involves child molestation, abuse, drugs and prostitution, etc. While no names would be mentioned, many of the author's family & friends know about this book and her past. While names can be changed, some of her family will not appear in the best of light. Using a pen name for the book wouldn't work due to the fact that people know her experience and the book. I had thought of getting people to sign a statement swearing they will not sue and are okay with her putting out this book however, she has informed me that she doesn't believe everyone would be willing to sign it. I would like to help this lady get her book out as I believe it is also therapeutic for her. I don't want her nor I to end up being sued however. I am looking for legal advice for starters. I am in Canada so Canada law would apply here. If documentation will be needed to be done for this job, then I would like that done as well. People with experience in this field and type of lawsuit only please. I set the bids for micro for the advice however I am assuming that you will bid higher if you plan to do paperwork. I am a starting up company here who is at the moment taking in author's free to better establish the company. Thank you!