Besides, Sylvia had all the time there was, and very little use to make of it. (1.2)
Ah, the beauty of childhood. But Sylvia is an exceptional case: There really aren't any kids around for her to hang out with.
It was a consolation to look upon the cow's pranks as an intelligent attempt to play hide and seek, and as the child had no playmates. (1.2)
Sylvia is so desperate for companionship that she makes a cow her best friend. This is indicative of how Sylvia has filled up the void of human companionship with a relationship with nature.
"'Afraid of folks,' they said! I guess she won't be troubled no great with 'em up to the old place!" (1.3)
It makes us chuckle to remember that Sylvia was born and raised in the city—in fact, she's only been living with her grandmother for about a year at this point. Seems like she was meant for this quieter life, though.
When they reached the door of the lonely house [...] Sylvia whispered that this was a beautiful place to live in, and she never should wish to go home. (1.3)
It turns out that Sylvia actually loves isolation. Rather, she loves isolation from people—we doubt she could be separated from nature without a shedding a few tears.
Sylvia [...] stepped discreetly aside into the bushes, but she was too late. The enemy had discovered her. (1.5)
To Sylvia, any stranger is an "enemy." If that doesn't tell you a thing or two about her mindset, then we don't know what will.
Sylvia was more alarmed than before. Would not her grandmother consider her much to blame? But who could have foreseen an accident as this? (1.8)
Again, Sylvia's word choice tells us everything we need to know. She stumbles upon a stranger—who seems rather nice and polite—and calls it an "accident."
She knew by instinct that her grandmother did not comprehend the gravity of the situation. She must be mistaking the stranger for one of the farmer-lads of the region. (1.10)
Sylvia is especially suspicious of the young man because he seems to be from the city. Sylvia might not be freaking out so hard if it were a fellow nature-kid (someone who lives in as much isolation as she does) but a city-boy is something worth fearing.
He gave her a jack-knife, which she thought as great a treasure as if she were a desert-islander. (1.26)
Slowly but surely, Sylvia begins to warm up to the young man. Her naturally introverted personality prevents her from completely buying into the things he says, however—she's not a savvy consumer of people. Not at first, anyway.
At last, evening began to fall, and they drove the cow home together, and Sylvia smiled with pleasure when they came to the place where she heard the whistle and was afraid only the night before. (1.27)
Now that the man isn't a stranger, Sylvia can look back and laugh at the fear she felt the previous day. Does she not love isolation as much as she thought? Was it wrong of her to give up city life for the isolated natural world?
Alas, if the great wave of human interest which flooded for the first time this dull little life should sweep away the satisfactions of an existence heart to heart with nature! (2.3)
Finally Sylvia realizes that she must make a choice between life among people and life among nature. And after much back-and-forth, she picks nature. Which would you choose?