Can my ex-wife sue me for writing about her in my book?

This is an interesting question. Your ex-wife probably does have certain privacy rights, in Oregon anyway probably a right to avoid the public disclosure of private, intimate facts, and the right not to be portrayed in a false light. You may also risk libel for things you say that aren't true. If your ex-wife is recognizable, that's enough to trigger the legal analysis. Of course, people could hardly read the book without being able to identify her. Of course, first amendment rights take precedence over privacy rights, but the first amendment at its core protects speech about matters of public concern like political speech. Here, you have speech about private matters. It isn't necessarily protected speech in a book. I'd go over what you write with a lawyer you can probably mediate a little to avoid these issues.

In basic terms, you cannot write about a living private figure without their permission. Changing her name is not enough if people could easily identify her as the character in your book. Normally, when writing about a living private person you must first obtain life story rights. This is because their life is not part of the public domain. In the end, this is an extremely complex area of law and I recommend that you consult with an attorney.

Yes, she can sue you and can probably keep the book from being distributed. I will assume you do not have a publisher and are thinking of self-publishing. You should get a good lawyer to advise you. If you want to write a personal journal, that is one thing. Showing it to others or publishing it in any way is probably violating the rights of many others in many ways.

She can sue you if you write anything about her that is false, defamatory or derogatory. It does not matter if you change her name. After all, she was your wife. Everyone will know who it is.

You can write whatever you like about your ex-wife and she can sue you for slander and libel as soon as the book is distributed. If you're going to write anything about her, whether you change the name or not, you'd better be able to back your statements up with objective evidence.

In the U.S. justice system, by paying a modest filing fee, anyone can sue anyone, for anything. The real question is can she prevail against you. It depends on many factors. Are you libeling her (i.e., writing lies about her)? If so there are grounds for damages. Most books are "vetted" to address liability concernsso should yours.