There is huge variation but a rough guide is on page 3 here ie between 3 and 5 for year 1. Most schoosl have a colour banding system across several schemes and "real" books of similar level of difficulty, age appropriateness and complexity.
hi my dd just finished, yr1 got2a for reading. she has a reading list for the hols. which contains following;
George's marvellous medicine I believe in unicorns Lion, witch & the wardrobe matilda Happy mouseday My naughty little sister series family phatoms little seahorse George speaks lion at school Crazy mayoonaisy mum akimbo & the elephants Harry the poisonous centipede Poetry paint box athologies
also she is currently reading the spiderwick chronicles - which she loves.
She will probably shoot ahead once she clicks with it, and once tht happens the books get more interesting and that will encourage her. Y2 will probably be the year she reallys 'gets it' so be ready! If you look in the library over this holiday they have a shelf for beginners and if you browse you will spot the ones at Stage 1/2/3 levels. I would have her read six of those over the holidays to help her out. We do a book at bed time and then a chapter that I read. I expect you do something similar. I can recommend The Faraway Tree and Rainbow Fairies to spark her imagination. That may give her a reason to learn.