What do you recommend for an advanced 12 year old reader?

[Coaster1]

But avoiding mature themes
She’s a voracious reader. Likes crime mystery type books , but I want to make sure that advanced books don’t mean older teenager themes
Am I asking for the impossible?
thank you!

I loved Sherlock Holmes at that age. " They were the footprints of a gigantic hound Mr Holmes!".
Actually I still love him. I was thinking about that story about the Cambridge student who cheats on his exam and Holmes let's him get off because he is going to go out to "Rhodesia" and build the strength of the Empire. When I read it I was impressed by Holmes lack of moral judgement!
I loved the way Holmes and Watson always carried firearms and never hesitated to use them. I'm not sure I am selling this to you now!

the Cadfael mysteries by Ellis Peters - first one is A Morbid Taste for Bones, second is One Corpse Too Many and should be read before any of the rest!
Ellis Peters also wrote a contemporary (at the time) series about Inspector George Felse. I don't think they necessarily need to be read in order, though his son ages through the series. I particularly remember Rainbow's End, The House of Green Turf, and Death and the Joyful Woman
Dorothy L Sayers - plenty of love and death and a bit of drugs and weirdness, in a twenties/thirties kind of way - pretty sure pre-teen friendly. Whose Body? is the first
Wodehouse isn't crime as such but has the convoluted plots

Some (by no means all!) of the SF&F is good for this kind of thing
the Chronicles of Prydain by Lloyd Alexander - first one is The Book of Three
The Earthsea trilogy (there are more now but I haven't read the later ones) by Ursula K Le Guin
The Dark is Rising sequence
Alan Garner - The Owl Service, Weirdstone of Brisingamen, Elidor, Moon of Gomrath
classic Asimov - some of the Robot short stories are kind of like crime mysteries?
CS Lewis - think I read the Screwtape Letters a year or so later, his "SF" trilogy definitely after that

Mary Stewart wrote what I think would be called romantic suspense - young woman, often in what at the time would be considered an exotic location, such as Greece, stumbles into a mystery and finds a love interest.

On Kindle, look for 'cosy' or 'cozy' (US spelling) mysteries. Lots being published in 'boxsets' at 99p or £1.99.

The Flambards books are really good for that age. I loved Monica Dickens too. The Shardlake detective books set in Tudor times.

Shardlake is far too complex, and gory in places, for a 12yo.

Have a look at the Year 7 and 8 suggestions on here https://schoolreadinglist.co.uk/category/reading-lists-for-ks3-pupils/

I was 14 when I first read it, and although it is one of my favourite books ever I’m not sure I’d recommend it for a 12 year old. It was the most adult thing I’d ever read and I devoured it over about 3 days.

For some reason it’s really stayed with me, and I think about it a lot, although it pisses me off when J. turns up with his giant magical healing penis. Yeah, maybe not for a pre-teen?

Lucy strange books. I just read. The ghost of gosswater Hall.....as an adult I couldn't put it down..its meant foe 8 - 12 years old..but I would think aimed at the upper range of that

Also the classic. The outsiders. By s e hinton

Echo @merryhouse I was reading Agatha Christie in year 6 so I'd also suggest Marjorie Allingham's Campion novels

DD is year 7, almost 12. She has recently loved The Hunger Games series, the Geek Girl Series and the Good Girl's Guide to murder series which she is currently in the middle of and loving.

Over the past couple of years she has enjoyed the Murder Most Unladylike series, Scarlett & Ivy series, the Sinclair Mysteries by Katherine Woodfine and Ruby Redfort.

My DD loves the Murder Most Unladylike series, she's 11.
I quite like the Miss Silver ones!

I have a voracious reader. I let them read what they want with the condition that I can pick up the book and veto it if it seems too adult.
They have enjoyed Murder most Unladylike, A Series of Unfortunate Events, The man in the Brown Suit, The Last Bear, His Dark Materials, several Terry Pratchett books and got started on the Heartstopper series.

DD started to get into the Classics at that age and we started her 'Beautiful Books' collection of clothbound hardbacks. Frankenstein, Animal Farm etc

She also developed a love of poetry and playscripts then too and loves Shakespeare, Romeo and Juliet, Macbeth, Hamlet are all good and familiar stories. There is a version of Macbeth with David Tennant on BBC sounds s she could read along as although she doesn't need the help hearing it performed is great.

Hunger Games and the Divergent Series are popular with that age group as is Skulduggery Pleasant.

I would be mindful of pushing too hard, reading for pleasure is important too it doesn't always have to be a 'worthy' book. Artemis Fowl -child criminal mastermind or Rick Riordan's books if she likes history are well written even if not a challenge. Along with Sherlock you also have the Enola Holmes series,they aren't long but are interesting