I've been debating whether to give this book five stars or four, but I think four is a better place to settle.
I don't always like books that mostly feature letters. This format inevitably leads to more 'telling' than 'showing' and that can make the read tedious. Dear Mr Knightley suffered from this, particularly at that start. It took a few chapters before I could engage in it. Sam was also a frustrating protagonist, particularly at the start. However, I liked her and understood the way she hid in books. I can relate to the 'quote' thing too, although I supplant my stock of quotes with lines from movies and TV shows in addition to books.
She was a little naive, particularly for a girl who'd been through a lot of foster homes, but maybe she just seemed that way because my own experience makes the kinds of things she missed obvious. I guess, if I'd had the upbringing she had, they may not have been so obvious.
I liked that the relationship she develops with her love interest was real. It was messy and problematic. I enjoyed that. So, if you can handle a book written mostly in letters, I recommend it.