This question could be referring to several different parts of the book, but I think that it is likely asking about the opening events in part one of the book.
Miyax is afraid because she is lost on the tundra of the North Slope of Alaska. Miyax is afraid of her entire situation, because she is also without food.
Miyax knows that her situation is fairly dire. She needs food, and she needs it soon. Her best option is to befriend a small wolf pack and convince them to share some of their food. She's lost in the Alaskan wilderness with no food and is attempting to befriend wild wolves. . . yes, she's scared for a good reason.
What's amazing about Miyax is that she isn't too afraid of the wolves themselves. She is afraid that the wolves won't accept her and help her. That's her main concern, because it means death by starvation.
Her hands trembled and her heartbeat quickened, for she was frightened, not so much of the wolves, who were shy and many harpoon-shots away, but because of her desperate predicament. Miyax was lost. She had been lost without food for many sleeps on the North Slope of Alaska.