The quotation provided in this question offers a creative example of a simile, of vivid imagery, of personification, and of hyperbole. Let's define these terms and look at how each of them works.
A simile is a comparison between two dissimilar things, one of which is known and one of which is not. In this case, the author is comparing the look on a person's face with the sun winking out. We've all seen the sun disappear behind clouds, so we have an idea of what it is like when the sun suddenly disappears or at least becomes much dimmer. This helps us understand the look on the character's face. Her face becomes dark (emotionally), and we can imagine that she is in some kind of distress or shock. The comparison allows us to relate the look on the woman's face (which we don't know) to the sun winking out (which we do know).
However, we can also identify the phrase “the sun had winked out” as both vivid imagery and personification. It is vivid imagery because it presents a sensory detail in language that helps us picture exactly what has happened. It is personification because the sun is winking; it is doing something normally attributed to a human being.
Finally, this quotation smacks of hyperbole. Whatever has happened to cause the dark, dismayed look on the woman's face, it cannot be as bad as the sun going dark and not shining again until next June. This is an exaggeration for effect, and it certainly serves its purpose of catching our attention and letting us know how upset and bewildered and shocked the woman is.