Is the syllabus for the piano prep test always the same? I have two boys who took the prep test a year ago and my daughter is now ready to take it but it looks like the same book.

Yes. It's still the same.

Yes, the main book is the same, although there is a wide choice of pieces for the second piece. If your daughter would like to try something different, maybe you could look at Trinity Guildhall Initial or one of the London College of Music pre grade 1 exams (3 levels).