A young man has arrived in the forest and told Sylvia that he will pay her ten dollars if she can lead him to a rare white heron.
Although she's torn, Sylvia decides to find the heron for the hunter.
She climbs the highest tree in the area, has a magical experience, and sees the heron.
So does she tell the hunter where to find the heron and collect her commission? Nope.
Sylvia runs home with dollar signs in her eyes but realizes that she physically can't "tell the heron's secret and give its life away" (2.13). It's never explicitly stated why she does this, but we'd peg her obvious love of nature as Exhibit A and her intense experience atop the oak tree as Exhibit B (for more on this tree experience, check out the "Symbolism, Imagery, Allegory" section—there's more there than meets the eye).
Although Sylvia remains in the forest, she never forgets the hunter, nor is she ever quite sure that she's made the right choice. Although Sylvia is a proto-hippie country gal at heart, she knows that the hunter represented a very different path her life could've taken, and as the story ends, she still wonders where it might have taken her. It doesn't exactly reek of regret, but seems more like a sort of forlorn daydream about what might have been. But hey—we all do that sometimes.