Quote Originally Posted by Valda View Post
How would you say that? Since it's a noun after a verb, you use accusative, right? But we only use it on нашла or also on книга?

Я нашла эту книга
Я нашла эту книгу

or maybe the accusative rule no longer apply once we use это?

Я нашла эта книга
Isn't there only one noun in the whole sentence?

"Я нашла эту книгу" is the only correct variant. If such sentences raise questions, I would seriously recommend throwing away whatever grammarbook you use, and consult An On-line Russian Reference Grammar instead.