My 14yo DD has always been a picky reader! Recently she’s enjoyed the Roman Detectives series - read all of them followed by Caroline Lawrence’s other series set in Roman Britain. She then read the Tamora Pierce Alanna quartet. I tried her next on a Dianne Wynne Jones (going down the fantasy route), think it’s called Hemlock and Fire, but she says it’s boring.
Sally Lockhart trilogy was scary - someone is killed in the first few pages to be fair!
I gave her Murder on the Orient Express to try (thinking along crime lines) but the print is too small…
she’s also enjoyed Lauren St Child horse books but always rejected K M Peyton horse books…