Ling Ling had gotten a book from her grandmother which is about the legendary battle of the 100 mages, which she is reading to Elise who is awestruck by the tale. Basically the 100 mages fought off and eventually defeated an evil empire and Ling Ling and her family are descendants of one of them. (don't worry, this book is just a child friendly version that Ling Ling's grandma personally wrote)

That symbol on the front cover is her family mage crest (most descendants of the 100 mages are permitted to change the crest of they want)