The care and feeding of an advanced reader is a tricksy thing (I have two myself and am a primary school librarian so this is a big chunk of my life). The problem is that literacy development is out of step with emotional maturity and life experience; give a book too early and they won't get the best out of it, making what is otherwise a great book deeply unsatisfying. And then of course you have the potential for unsuitable material. Because of my job I managed to read and discuss most of what my eldest was reading at around 11 and it's set the foundation for a lovely relationship - I know I can trust her to come and talk to me about anything she finds unsettling (she's 13 now and eg able to spot unhealthy relationships, which YA is frankly riddled with).
I'm currently feeding my advanced Y5 & Y6s any and all of the following authors depending on their tastes:
Christopher Edge (sci fi)
Emma Caroll (historical, lots of time periods to choose from)
Padraig Kenny (robots)
Sinead O'Hart (adventure)
Francis Hardinge (creepy historical)
Katherine Rundell (adventure)
Lisa Thompson (contemporary/issues)
Ross Welford (contemporary/issues - particularly lovely if you live in the NE)
Stewart Foster (contemporary/issues)
Gill Lewis (contemporary/environment)
David Solomons (humour)
Sylvia Bishop (contemporary)
I would look at Pullman, Cathy Cassidy, James Patterson, Geraldine McCaughran, Piers Torday and Lauren St John too. Handle Pratchett with care. The Tiffany series has a young protagonist, yes, but the third in the series opens with a pregnant teenager being beaten so hard by her father that she miscarries. It should not be on the 8-12 shelf. This is a good rule of thumb for any series where the characters grow up over a number of books - your voracious reader will want to gobble the series within months, but won't be ready for the emotional challenges encountered by an older main character. I've had to stop stocking a particular series after six books because the main character's relationships have become unsuitably grown-up at 15 for my readers of 7-11.
There are many more fantastic books at the top end of middle grade before you step into YA, those are just the ones I've had budget for this year and I know they do the job.
I would honestly avoid things that you remember reading in high school English. Chances are she'll end up doing them herself and it's immensely tedious to repeat a novel when you're an advanced reader (yes, I was that child too).
Also don't assume that always "reading up " is the right thing to do. Kids do just fine with a range of books - "easy" books read repeatedly can offer new insights as children grow. Age-appropriate graphic novels are brilliant for visual literacy (understanding how pictures and words combine to make a story - the basis of newspapers and adverts). Go wide rather than high - and never underestimate the power of non-fiction, either.