Fairy Treasure by Gwyneth Rees
Connie is not a child who likes books. So she's not too pleased when she's sent to stay with her eccentric author aunt. But then Connie meets Ruby -- a book-fairy -- in the dusty old library. Ruby is in trouble: she has broken fairy-law by trying to take something -- a piece of jewellery -- back to fairyland through the 'gateway' of a fairy-dust-sprinkled book. And now the jewellery has disappeared and Ruby can't get back home!
Can Connie help Ruby find the missing jewellery before the doorway to fairyland is closed forever?