This book is one of the main books in the series to cast a conspicuous spotlight on the failings of our main group. There's never a book where they're completely infallible and where their human nature doesn't cause them to make at least one mistake, but this one highlights what can happen in those situations a lot more than most of them
Rachel's insistence on being an autocratic leader and not being willing to change her strategy almost gets the team killed multiple times, and we see her - rightfully - called out for it. We also see her accept that this isn't something she's good at, which is quite a powerful message for kids reading this for the first time
The fact that a civilian died because of her actions and what she forced the team to do clearly weighs heavily on her, and in the end she's not even the one to defeat the primary villain of this book.