If you don't like people, they can't hurt you. Almost-8-year-olds who are often described as "different" learn that very quickly.
That lesson was impressed upon Elsa pretty hard, which has left her with a very small group of people that she likes (but, like most 7 year-olds, she really wants to like people) -- although in many, there's only one person in that circle for Elsa -- her grandmother. Elsa's grandmother was her best friend, her superhero, the most devoted adult in her life.
Elsa doesn't do that well in school -- doesn't get along with teachers or classmates -- but thanks to wikipedia, knows all sorts of things in very random areas. She's utterly convinced of the importance of the Harry Potter series and other "quality literature," like Spider-Man comics.
She used to write letters to Santa every Christmas, not just wish lists but whole letters. They weren't very much about Christmas, mainly about politics. Because Elsa mostly felt that Santa wasn't involving himself enough in social questions, and believed he needed to be informed about that, in the midst of the floods of greedy letters that she knew he must be receiving from all the other children every year. Someone had to take a bit of responsibility.
Following her Granny's death, Elsa is given a series of letters to deliver to various people that her Granny has helped in the past, but who've had problems with her since. This eventually involves adventures (things both 7 year-olds and adults would consider adventures) and a lot of personal growth. As she delivers them, Elsa learns a lot about who Granny was before Elsa came along, and finds herself in a much larger world than she'd previously been able of living in.
This is just charmingly written, sweetly told, and it'll draw you in with the language. Backman and Koch show a delight with language and people that will surely win you over. It'll make you smile, it'll make you giggle, it'll make you melt a little -- if your grandmother's alive, you'll want to give her a call -- if not, you'll miss her more than usual.