I found for my DD6 letting her take the lead in when she wanted to read the longer/advanced books worked best. I think she could sense that I wanted her to move on from fairy/princess books and so resisted quite a bit (she is very self directed and independent). she also preferred advanced books with complex stories but wanted us to read it to her.
Roald Dahl books were the turning point - she loved them so much she picked up where we left off and has been reading longer books since (secret garden, the Penderwicks etc). She reads all the time but will alternate from book to book unless she finds one irresistible. It also helps that her older brother is an advanced reader and she wants to read (actually do better than) what he is reading.
Currently she is obsessed with captain underpants unfortunately!!
