The paragraph lies below in italic, it's an excerpt from a novella by Stephen King.
And he looked at her reproachfully. It would be a little while yet before she picked up the book and threw it at him, but that was what really tore it. That reproachful look. She could no longer stand it.
I have trouble with understanding the bold sentence. I assume meaning would be something like "as soon as he glanced to her, she flung the book at him". But usage of three conjunctions (while, yet, before) in a row confused me. I think "while" in this sentence is used as main conjunction and "yet before" is a synonym for "just before", indicating that there is only a small interval between two incidents. Am I right, or did I just digress too much from actual meaning? Is "yet before" a legitimate use in English?