Yesterday, I found out via Kellen Hertz's Facebook page that Courtney's second book is releasing in March 2021. Now, I know more about the plot about the book from AG Publishing's website and the last page of Courtney's first book!
According to the Courtney Changes the Game Teacher's Guide, Courtney's second book will be titled Courtney: Friendship Superhero.
In an overview of the entire series on American Girl Publishing, it says this about the events of Book 2: "But life outside the arcade is complicated—her dad gets a new job and schedule, her stepsister becomes Courtney’s reluctant roommate, her mom starts a campaign for mayor, and her friend comes down with a frightening disease. It’s a whole new game for Courtney—and she’s trying to figure out the rules as she goes. Can Courtney power up her inner hero to meet the challenges ahead?" We can assume this frightening disease is AIDS, since the AIDS crisis was a big deal in the 1980's.
But that's not all! In one of the last pages of Courtney Changes The Game, a full summary of Friendship Superhero was posted. Here it is!