I'm 60 years old and, in the past year, have read Agatha Christie's Poirot books, Richard Osman's whodunnits, The Naughtiest Girl in School by Enid Blyton, Harry Potter, Percy Jackson - Rick Riordan and Derek Landy (Skulduggery Pleasant), The Handmaid's Tale, Lord of the Rings and two Janice Hallett whodunits along with some authors whose names I've forgotten.
A few weeks ago I was clearing out some of DS's old books and came across his Thomas the Tank Engine books, sat down and enjoyed a load of them. Happy memories.
I don't think any of the above have helped or hindered my intelligence to be honest.
As long as she's reading a cross section of books you should be happy. Some of my books push my thoughts, others just make me happy (like a comfy pair of socks or a bar of Galaxy). Horses for courses.
DS, who is starting his GCSEs any day now, has reverted to reading Lego magazines and anything Star Wars! He's had enough of Dickens, Shakespeare and the modern classic he's had to analyse to the final full stop. He just wants to relax.
Just be pleased she's reading. I work with some secondary school students who see reading as a punishment or boring. One said to me what's the point of reading, they'll be working for their dad when they leave school and he doesn't read much. If they picked up Dork Diaries from our library, I'd dance around the school!