While at The Mary Sue, Maggs sold her first book, The Fangirl's Guide to the Galaxy, to Quirk Books. It was published in 2015. A second edition, titled the Fangirl's Guide to the Universe and featuring updated text and new illustrations, was released October 27, 2020. A companion guided journal, The Fangirl's Journal for Leveling Up: Conquer Your Life Through Fandoms, came out on the same day.
