The Uncommon Reader by Allen Bennett (2007).
While dealing with unruly corgis, Queen Elizabeth II discovers a bookmobile parked by the kitchens at Buckingham Palace. Feeling that it it impolite to leave without borrowing a book, Her Majesty selects one and, again feeling it her duty, reads it. Soon, the aged sovereign develops a royal literary thirst as she devours tome after tome. She is carrying a book everywhere and is driving her staff to distraction as she shows more interest in her latest line of literary inquiry than her monarchical duties.
A short and gentle novella, The Uncommon Reader takes the unusual step of having a living monarch as the protagonist. It's a two-pronged story about the isolated nature of being Monarch of one of the world's great powers and the nature of reading. On the one hand, we have a queen who has always done her duty, was witness to the great events, and spoken to all the great, good and ghastly, but has never had the real opportunity to develop intellectually. On the other, we have an examination of how reading both uplifts and isolates; of how it improves, but is only a step in a journey.
Charmingly written and with a neat little sting in the tale, The Uncommon Reader raises a smile instead of a laugh, but it is well worth tuck into the book bag.