This book was written by someone who doesn't understand western riding, so she screws up in evaluating western saddles. For example, in her section on different types of saddles for cutting, barrel racing, etc, she starts each section with 'the goal of the saddle is to keep her balanced over her feet', then she criticizes the saddle type for not doing this - but her goal is wrong. Cutting, for example, doesn't WANT your feet under you. Neither does reining.
She then claims that moving your feet forward puts more weight on the rear of the horse, which defies physics. Moving body parts forward moves weight forward. It doesn't move your center of gravity aft. Nor is a western rider bracing in the saddle, pushing against the cantle when riding like that - he is settled in the deep part of the saddle, legs forward but not rigid and braced. The legs move forward, but the butt stays put - so the balance point moves forward, not aft.
Her discussion of endurance saddles suggests an English saddle may be required because the bars on a western endurance saddle may be too short to distribute weight, while ignoring that the saddle works as a whole to distribute weight, and that western saddles distribute it over a much larger area than English - thus less pounds/sq inch. Also, a short Western saddle is usually longer than an English saddle.
Her discussion of saddle trees centers on "Arizona bars" or "Northwest bars" - good luck finding anyone advertising a saddle for sale with "Arizona bars". I've never, ever seen a saddle advertised thus. And in discussing flex trees, she seems to miss that flex trees try to modify a stiff piece of plastic to give it the same flex as a tree made from pine & rawhide - thus missing the entire point of flex tree saddles. They restore the flex, not give it new flexibility.
Saddle types don't exist independent of equitation. You cannot understand saddle design and fit without also understanding how it is affected by the corresponding style of equitation. FWIW - I ride English, Western and Australian saddles, but I don't ride them as interchangeable. Each has its own corresponding equitation, and riding English style in a Western saddle is as much a mismatch as trying to ride dressage in a jump saddle - you can do it, but you end up fighting the saddle.
Saddle designers are not stupid. They design saddles to support the sport and style of riding, and the author of this book doesn't understand that! Her book on English saddle fit is imperfect, but not grossly wrong like this one is.