Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Apathetic Disdain
We get the narrative through the "lens" of the narrator's own thoughts and memories. She's a fairly passive and unflappable, even in the face of things that you would expect to upset her a lot. For example, when David and Anna, her supposed friends, decide to mock her mercilessly (and pretty nastily) for not succumbing to David's "charms," she doesn't react at all.
That said, don't be fooled into thinking that her ability to rise above conflict means she's some kind of super-positive goody-goody—quite the opposite, in fact. Overall, it seems like the narrator thinks that things kind of stink, but she feels powerless to change them. A good example of her attitude can be found early in the novel, when she describes the bar where she and her friends stop for a beer before heading to her family's cabin:
It's an imitation of other places, more southern ones, which are themselves imitations, the original someone's distorted memory of a nineteenth century English gentleman's shooting lodge, the kind with trophy heads and furniture made from deer antlers, Queen Victoria had a set like that. But if this is what succeeds why shouldn't they do it? (3.14)
As you can see here, she paints kind of an ugly picture of the place, and her use of words like "distorted" and "imitation" hint at a certain amount of disdain for the place. However, she steps back from really passing judgment, basically throwing her hands up and saying, "Well, if they like it…" If you've ever heard someone use that phrase to describe someone's wedding dress or other outfit choice, you know it's faint praise indeed—and that kind of half-hearted, half-disdainful "positivity" is the best we get out of the narrator most of the time.