I think it depends what the purpose of your book review is, what your relationship is with the author (if any), and who your audience is. I have read books that were well written but on topics that did not interest me, and I have read books that were written very poorly but for whatever reason were an enjoyable way to pass the time (for example, anything by Danielle Steele). If I am understanding correctly, the book you want to review is a memoir so I think it matters whether the particular person is important to you and whether the purpose of the book review is to support the author and if not what the purpose of the book review might be. I also think it matters whether the memoir is lighthearted or instead covering very heavy topics.
Is your critique that the book is poorly written? Or does the memoir contain lies or misleading information? Were you asked to provide a review or do you feel called to write one? I really do think the tone of any book review would depend on the motivation to review the book.
I am reminded of a memoir of sorts that I read by Suzy Favor Hamilton, an Olympic runner who eventually became a highly compensated escort/prostitute and now holds herself out as a proponent for mental health. I read her book "Fast Girl" anticipating insight into her mental health struggles and how she had overcome them and how she can help others who may have similar struggles. Her memoir was NOT that and came across, to me, as more bragging about how hot she is and how she was the best runner and then the priciest call girl in all of Nevada, etc. It was somewhat jarring. If I were to write a book review of her book I would likely be honest about how she came across as narcissistic and not in a healthy place, in my opinion.
But if Suzy were a relative or friend, I would not likely write such a public review of her memoir. I probably would decline to write a review of her book. I might reach out to her privately to discuss my perception of how she came across (to me, anyway) in her book, but unless I was pretty close to her I probably wouldn't unless she asked me.