I don't get what she means. She reads a shiny book, it goes unshiny and her wisdom stat increases. Her friend tells her that the same thing happened to her when she read a shiny book. So how did she come to the conclusion that your wisdom stat doesn't increase whenever you read a book?
Am I missing something?
Edit: I read this part in the novel and the line she says there is "The books in this place were not the only ones that could increase your stats?" which has a completely different meaning than "I guess the wisdom stat doesn't increase for every book."
So either the adaptation of this line from novel to manga is bad, or the translation of this line from Korean to English is bad.