Whew, I've no desire to be harsh in a review of a children's book, but it might be difficult here. I'll do my best to be constructive rather than giving in and just ranting.
I think I understand what the author was trying to accomplish with the ridiculous over-the-top-ness of everything here. It seemed as though she was aiming for satire, which may actually be my biggest issue with the work. There are certain stories and certain genres in which satire is delightfully appropriate and helps illustrate certain ridiculousnesses that we've come to accept as the norm. A children's book, in my opinion at least, is not one of those appropriate places.
On top of which, the satire was handled with such poor grace and heavy-handedness that it made the characters seem boorish and hateful rather than silly and countrified (as I'm hoping was the intent, anyway).
The stereotypes were over-stereotyped in such a way that it was clear the intention was humor. Agent Agent, for example, or the too-perfect-to-be-real Dr. Hellion, not to mention Piper's parents or the improbably named country folk. And the attempts to go against stereotype (Nurse Tolle, the former professional linebacker nicknamed "Bone Grinder," for example) were just too heavy-handed to be funny.
I think my biggest issue, however, is that in other works I've read where stereotypes are played on in such a way, the feeling behind it is one of fondness, of the type of gentle mocking you'd give a good and trusted friend. The feeling behind this felt more like a cackling glee at the chance to show the world the unbelievable ridiculousness of these types of people. And that's just not the feeling I want to have to have while reading a children's book. And not one I'd like for any child I know to have to deal with, either.
Wholeheartedly not recommended.