My 13 YO avid reader of a daughter says:
Sophies world is ok, but quite philosophical and some quite tough ideas, though some good life lessons.
she recommends a streetcat named bob, as its a very positive story though covers some mature stuff (about someone overcoming drug addiction)
if she’s into wildlife/outdoors – a year in the woods, written by a fc wildlife ranger (contains deer culling etc)
she says ‘theres a boy in the girls bathroom’ is very funny
Louis sachar’s ‘holes’ is always a great one, and the wayside school series books are great
factual wise, she says:
ripleys believe it or not, but with some uuurrgghh moments, though not dark
‘why is snot green’ and the associated series, very good science introductions
Ben Goldacres bad science she loves, bit geeky but teaches to read between the lines