Binkie, you are so elegantly tactful! I think that is a masterpiece.
But worth checking what the arrangements are for doling out the reading books. We've had variations on
Book selected by teacher
Book selected by teaching assistant/random parent/playground supervisor, obviously all with variable results
Books chosen by child from completely inadequate range in classroom
Book chosen by child according to inappropriate 'levelling' to which child has been assigned by TA who would need annotated diagram to find various parts of her anatomy
Book chosen by child from full library range
The latter is obviously the best for a fluent reader, but to get there we had to make sundry representations to teacher/deputy head to get dd1 (then in Y4) classed as officially off the top of any reading level, and therefore allowed to exercise her own judgement in choice of book. Before that Harry Potter was officially classed as too difficult (white level) despite the fact that dd1 was reading Lord of the Rings at home. Barmy.
Having said that, child's own choices can sometimes be a bit eyebrow-raising. Dd1 went through a phase of choosing Captain Underpants (particular hate of mine), and appallingly horrible books by Robert Swindells, which IMO are completely unsuitable content-wise for primary-age kids. But having made such a monster fuss for her to get free access, I could then hardly complain about content.
Of course what you want is a wise, book-loving dedicated librarian-teacher, who actually reads children's books, chooses them specifically for all the groups that use the library, and gently guides children to extend their choices, in some cases across the adult-child divide (Frost in May, anyone? I capture the Castle? etc etc.)
But it won't happen.
I think all you can do is make as much fuss as your relationship with the school will take. Or take matters into your own hands: ds (Y2) is a fluent reader, one of at least 10 in his class, but having weedy little banana books imposed on him by one of the playground supervisors who has been charged with changing Y2 books (wtf?). In the end I took action, lobbied other likely parents in the class to hand over their spares, raided my own selection of spares and 2nd hand books and put together a box of 'proper' books for that age group (HP, Dick King-Smith, Flat Stanley, Horrid Henry etc etc.).
Teacher now loves me to bits, as she wasn't at all happy with the existing arrangement, but had no means to change it.