Magical Library where you can enter books

I read a book a while ago where I think the main character was a girl, and she goes to a library and can enter books and at some point she gets chased by monsters in the books. Pretty sure main side character is a boy and there's an old guy librarian. There were definitely sparkles at some point entering/exiting a book. Also, I think she wasn't supposed to enter the books? Please help!

This sounds like The Book That Wouldn't Burn by Mark Lawrence

Some overlap with The Night Librarian.