Jane Gardam has become one of my reliable authors -- she has written lots of books, I have a pretty good idea of what I'm going to get when I crack one open, and I can be confident that I'll enjoy the ride. (Side note: I wonder if early Kate Atkinson was influenced by Jane Gardam?)
I hadn't come across Crusoe's Daughter (1986) before, but it's vintage Gardam. Ostensibly it's the story of Polly Flint's life, but about three quarters of the book deals with her childhood and youth; Gardam especially excels at depicting awkward, eccentric teenage girls, surrounding them with even more eccentric, sometimes grotesque characters (most often forceful women and timorous men), and throwing in a massive twist at the end of the book.
Polly moves to the Yellow House by the sea, surrounded by marsh, to live with her aunts when she is four years old, and remains there for the next eighty years while wars rage and the town grows up around the house, swallowing the marsh, and the outside world advances and recedes like the tide. Polly is also obsessed with Robinson Crusoe, and there are many parallels between Polly's isolated life in the yellow house and Crusoe's stay on his desert island. Polly is another character who is involved with/obsessed by a fictional character (the inevitable irony being that she is fictional, too).
Mind you, I just asked my 17 year old if she knew anything about Robinson Crusoe, and she said she's never heard of him, so perhaps Polly's confident prediction that his fame would live forever might be misplaced?