There are youtube videos with the author Deborah Feldman, who now lives in Germany. This book does not at all seem to have been a hoax. That rumor may have been started by members of the Chassidic group that she left.
As to the show on Netflix: to the best of my understanding, the scenes that dealt with her time as a member of the community were based on the book, the scenes that deal with the time after she left that community are fictional.
Brooklyn, New York, USA