How about some classics? Plenty of gothic goodies if she enjoys Twilight (Try the Host by the same author, I thought it was much better!) and Wordsworth classics are only £1.99 through Amazon. Jane Austen is also challenging without being too racy, although I guess you're happy with her reading some racy stuff if she's reading Twilight. Charles Dickens is a great place to start with epics too, especially if you've seen an adaptation on BBC! Anthologies of short-ish stories are also a great way to find out what you like. Can highly recommend 'the mammoth book of' series. Very much aimed at adults, yet some would be suitable. Try fantasy, sci-fi, and even manga this way! Other older titles that might suit include 'A Town Like Alice', 'The Diary of Anne Frank', 'Wuthering Heights', 'Just Henry' and 'Cat's Eye'. Try also asking in your local library (yes, I've said it before on forums... and I don't work for the library!). The staff there are well aware of what would be age appropriate, and can point you in the direction of some different things. And nothing lost if not her cup of tea either. Hope this helps!