Dune is sort of appropriate--depending on how you feel about a series of novels all premised on wars and political maneuvering over an addictive hallucinogen.
I did read the original trilogy at about this age.
My ds loves sci fi and read Dune when he was 11. I am *not* a sci fi fan so I've never read it, I just picked it up for him off of a big stack of books that included Jane Eyre etc on a B&N sale table thinking it looked like something he'd enjoy! (That's what happens with parental oversight when you've got 3 kids and two of them are 2e and all 3 of the kids plus their parents have crazy-busy lives lol!).
DS loved Dune and had a habit of reading it any chance he had, including while walking. One of the adults at his school who had read it in college and loved it saw ds reading it and was impressed... and... also asked me if I really thought he was ready to handle the maturity of the themes.... which of course I knew nothing about lol! By that time ds was already almost finished, and assured me he'd had no issues with it.
How's that for non-advice?
FWIW, my 13 year old is an avid reader and prefers popular fiction - not sure if your dd would be into anything she's into or not, but in an attempt to find her books that lasted a few hours longer than all the John Green books, I suggested a Jodi Picoult book and she loved it. You'd probably want to pick and choose those based on what level of mature themes you think your dd is ready for - but in general, another thing I've done with my dd is to think back through books I've read in my book club, or for both my dd and ds when they were around your dd's age I'd look through lists of recommended high school books or high school curriculum lists. I also found that it helped for me to occasionally throw a book at my kids (not literally lol!) that was in a genre outside their currently preferred narrow genres and tell them they had to read the first two chapters but could stop after that. They rarely stopped - it just took that small bit of nudging to get them to read something that they were thinking wouldn't be interesting to them.
Best wishes,
polarbear
