I suspect she gave the go-ahead for the project and a book was ghostwritten for her, she probably doesn't want to endorse it but there are contractual obligations for it to go out etc. I suspect the various factions that look after her interests are in dispute and the project is being buried for that reason. People who write books are always very keen to share them. I will therefore conclude that Billie Eilish hasn't written a book, someone else has, and she doesn't like it very much. :o)