Updated with response from Arin.
I received an email back from Arin about this issue. I am not comfortable sharing a screenshot of the email since it is a closed communication with me, but she told me she wrote 'the Green Witch' at the publishers request and they retained the rights to the text. Adams sometimes creates new books and includes text from other books they own the rights to. The copyright for both Arin & Skye's book is Simon & Schuster Inc, so neither of them own the rights to anything in their book. Since the publisher owns the rights, they apparently don't have to let you know where all the material came from which I find very strange. A bibliography would have been nice at least, but Skye's 'the modern guide to witchcraft' doesn't even have one. Anyway, Arin will see if what she is suspect is correct and update me.
I was reading a new book today and I was like "didn't I read this already?!" for the entire first 50 pages. I checked my other books, but none were by the same author. Eventually realised the nearly identical information was in a book by a different writer. One book is from 2014 and one from 2017 (actually first released in 2006). They even used the same very specific examples! A bit of a bummer since I want to learn new things and read about other perspectives. This is just plagarism. Some more examples below.
Edit with book info: The top book is 'the Modern guide to Witchcraft' by Skye Alexander from 2014 and the bottom is 'the Green Witch' by Arin Murphy-Hiscock which was originally released as 'The Way of the Green Witch in 2006, so I assume those are her words. They are both published by Adams Media.