The land's new ruler did everything in her power, but the strange mother-of-pearl mist proved stronger. Now she has only one way out: to save all she could still save by leading the country's inhabitants into a new, unknown world.
An MLP and Anne McCaffrey's 'Dragonriders of Pern' crossover.
This book is a sequel to Outcasts. It features characters from that book series. So if anything seems unclear, you can read it in those books. :-)
P.S. I realize that the text contains a lot of Russian cultural references. Unfortunately, it's not always possible to find exact English equivalents, and sometimes it's completely impossible. If anything is unclear—please ask. I'll do my best to answer.
Russian version of the book: https://ficbook.net/readfic/10862451