While Amelia Earhart did have a sister called Pidge, the book is clearly fictional. It is, however, extremely well researched. Details of daily life in the 1960s are spot on, with the possible exception of Pidge wearing slacks in her 70s. None of the women in my life wore slacks during this time period, but I lived in Ohio and not on the fashion forward, daring west coast! Readers are also introduced to information about Earhart's travels and childhood in a way that will encourage them to seek out books like Candace Fleming's Amelia Lost.
Bea's relationship with her grandmother is also just right. The two haven't been close, but soon warm to each other's eccentricities. Middle grade readers who have spent a lot of time with their grandparents often find them to be the most sympathetic adults in their life, and those who don't know grandparents well often long for them. Bea's confusion and delusions are serious but not dangerous, but middle school is often a time when readers see grandparents becoming more frail. I liked how Behrens handled the grandmother's condition, and the portrayal of the divorce and step family will also speak to the experience of many readers, or give them insights into how other families live.
Like Blume's Julia and the Art of Practical Travel or Bustard's Anywhere But Paradise, The Last Grand Adventure transports family drama into an interesting and vibrant time period and shows us that while fashions, types of travel, and acceptable breakfasts (sugar sandwiches!) have changed over the last 50 years, family ties have not.