Memoirs are always difficult because not all narrators are reliable and it's one person's memories and experience. That said, I think Mathieu is not an unreliable narrator and this really was her experience. The Twelve Tribes is disturbing, but the picture she paints doesn't include some of the more lurid or extreme rumours I've read about. It was also more believable because she showed how things weren't equally oppressive and negative in all of the places she lived; some were much better than others.
I live in a region where there is more than one TT location so have taken it upon myself to visit two of them, both on Friday nights and Saturdays to see things for myself and not just go by what is out there on the internet. Even if they are putting their best foot (feet?) forward it's still possible to spot things. Even I could see that the kids on one location were more free to speak up in a meeting than in the other and that there was a wee bit of variation in the skirts (one had only solid print skirts, unless they changed the rules since this was over about a year) but the same pants. In one group, only women did the cooking for the Friday night Sabbath meal but men helped serve; in the other, smaller one, an entire family did the cooking and serving--in both it's rotated by three teams, which I think is mentioned in the book.
But this is a review of the book. Overall, well done, and I think anyone who wants to learn about the Twelve Tribes should include it in their search, but it's important to question everything and talk to people who love it there (there are some and it's obvious they do), and if you're going to read their literature and have never read the Bible then be very careful before you accept what they are teaching because they take many verses out of context and they are, without a doubt, a controlling group, and the first red flag is them asking people (not forcing them outright) to give them all of their money and assets and to work for having their needs met. But it's interesting to see why some people went there who were longing for something all of their lives and are still there decades later.