Well, the fact that the narrator never gets a name is our first clue that she (and what she's about) is going to be a bit hard to pin down. She seems to kind of live within her own head, not really sharing that much of what she thinks or feels with her companions on the trip, and she doesn't let what they say or do really affect her. Her coolness in this regard helps her stay chill and stoic even in the face of pretty crazy stuff—for example, the discovery of her father's death and news of her boyfriend's infidelity. That's probably why her "friend" Anna calls her "inhuman" (18.51) and "cold-blooded" (7.31) at various points. Of course, the narrator doesn't let these labels get to her.
Of course, part of the reason the narrator might come off as inhuman is the fact that she just simply doesn't like or relate to humans all that much. In fact, she seems much more comfortable with people if they are animal-like or less evolved—like Joe, for example:
I remember the hair on Joe's back, vestigial, like appendices and little toes: soon we'll evolve into total baldness. I like the hair though, and the heavy teeth, thick shoulders, unexpectedly slight hips, hands whose texture I can still feel on my skin, roughened and leathery from the clay. Everything I value about him seems to be physical: the rest is either unknown, disagreeable or ridiculous. (6.24)
Here, the narrator seems imply that evolution's continued "improvement" the human race (by bringing about universal male pattern baldness?) is not really her cup of tea; she likes things to keep things "vestigial" (ancient by evolutionary standards).
The narrator's reaction upon finding a dead heron provides further proof that she connects more powerfully with the animal kingdom than her fellow humans, since the discovery of the corpse yields a bigger reaction from her than basically any of the other bad stuff she's had to deal with up to that point (much of which—like her relationship or her missing father—was arguably more serious). By "reaction," we mean that she actually seems to get angry:
Why had they strung it up like a lynch victim, why didn't they just throw it away like the trash? To prove they could do it, they had the power to kill. Otherwise it was valueless: beautiful from a distance but it couldn't be tamed or cooked or trained to talk, the only relation they could have to a thing like that was to destroy it. Food, slave or corpse, limited choices; horned and fanged heads sawed off and mounted on the billiard room wall, stuffed fish, trophies. It must have been the Americans. (14.7)
Going forward, the narrator's thoughts return repeatedly to the heron and the senselessness of killing it.
She might take the heron discovery a bit harder because she relates to being on the wrong end of mankind's tendencies toward destruction and domination. Thinking about men and relationships, the narrator laments her perception that everything is about victory and winning with the opposite sex: "Prove your love, they say. You really want to marry me, let me f*** you instead. You really want to f***, let me marry you instead. As long as there's a victory, some flag I can wave, parade I can have in my head" (10.28). Man—no wonder she wants to hang out with the animals over people.
We don't realize it right away, but the narrator isn't exactly the most reliable storyteller. Our first clue that her memories are a bit off comes when she starts talking about the baby she has left behind (not just for the trip—like, in general) with her ex-husband: "I'm waiting for Madame to ask about the baby, I'm prepared, alerted, I'll tell her I left him in the city; that would be perfectly true, only it was a different city, he's better off with my husband, former husband" (2.41).
Although initially referring to the baby as "him," she later veers into using "it" consistently, which seems more than a little odd. At first, it's possible to chalk the weird pronoun use up to the narrator's general chilliness and alienation from everything, and everyone, around her. Of course she would refer to her baby as an "it." Later, however, we learn that the narrator never even had a child; she had had an abortion rather than carrying the pregnancy to term, and she suppressed the memory. We also learn that this supposed "ex-husband" was married—just not to her. So, she definitely gets the details of that part of her life scrambled, seemingly to protect herself from stuff she didn't want to think about.
Confronting the truths in her past seems to represent the narrator's first step in taking control of her life and feelings. She says as much, opening the final chapter with the words "This above all, to refuse to be a victim. Unless I can do that I can do nothing. I have to recant, give up the old belief that I am powerless and because of it nothing I can do will ever hurt anyone" (27.1).
It's true that the narrator's lack of awareness of her own emotions has been confusing and hurtful to Joe since the beginning of the novel. However, when the narrator remarks in passing in the final paragraphs that she loves Joe, it appears those days might be over—though of course we never really find out.