The Last Grand Adventure by Rebecca Behrens
Beatrice is having trouble blending in with her father’s new family. It just doesn’t work for her to have a little sister. When the option comes for her to stay two weeks with a grandmother, she hardly knows in a retirement village in Arizona her dad and stepmom don’t seem sad to see her go. Anyway, her grandmother is Amelia Earhart’s sister. Amelia Earhart was an aviation adventurer who disappeared forty years before this story started. But the grandmother claims to have letters from Amelia and has plans for her and Beatrice to travel to Kansas to meet up with her. They don’t plan to tell anyone, and they don't intend to let their lack of money or grandmother’s lack of mental clarity get in their way.