I tried to find a detailed age recommendation but couldn’t find anything. But one reader said they had read it in elementary school and liked it. Another one remarked that the book was pretty thick, plus the fantasy theme made it hard for them to start reading. So maybe check back whether the girl in question likes fantasy and has experience reading longer books? Other than that, so far I don’t see anything that would make it unsuitable for a 10-year-old.
Also, I can definitely recommend Koteki no kanata for a girl around that age - if she likes fantasy. Zenitendo should also be a good match. And once she is a bit older, Kemono no souja should also be a good recommendation. (The world building might need a bit of stamina, that’s why I think that maybe age 12 might be more suitable? But not sure, it’s quite a while since I was 10
and it depends a lot on the person.)







