The Secret of the Ice Castle by SeriesDude is fan fiction based on the Dana Girls Stories. It can be found on wattpad. It has 21 chapters and it a complete book. Since the requirements say in any format, I will consider this to be the equivalent of an e-book. I believe SeriesDude is a friend that loves series books and has written other fan fiction.
It is well written, stays true to the Dana Girl Stories and has a realistic ending. If anyone is interested in reading this they can join wattpad and choose it for their library.