Stub pianoloverus The most important part in solving problems at the piano is I think figuring out what's causing the problem and what one should do about that. Playing small sections, playing some fixed number of repetitions, taking breaks during practice or for days on which a piece is not practiced, and some of the other things I've read on this thread that are in the book can all help. But I think they are often insufficient.
I have not read the book, either, but from biographical information and some of the videos, I understand her to be an advanced viola player. Her methods for practice are general and aren't limited to particular instruments. But I do get the impression that she is addressing practice by intermediate to advanced students, in which case the student should already be demonstrating some skill at problem solving. Her practice method is more about scheduling of practice sessions to match neurocognitive states than for problem solving per se. How to practice rather than how to gain skills.
Yes I agree that her book is probably mostly about what you say in your last sentence. And I think some posters give the impression that they think problem solving isn't nearly as important as all the things discussed in her book but I think problem solving is far more important.
I did see one post where the poster said something to affect they concentrated on one measure and figured out some new hand motions to improve their playing of that measure. I think that's the most important thing. Now if before reading the book they didn't realize they might have to work on a single very difficult measure by itself then the book is valuable as long as they could figure out better hand motions.
Without the ability to analyze what the problems are and figure out solutions this reminds me of the many books I saw when I was teaching math about how to "beat the SAT". All the little tricks and test taking techniques they mentioned were certainly reasonable, but without the appropriate mathematical knowledge I don't think they would improve someone's SAT score very much. They were the icing on the cake but not the most important thing.