Wherever it was that she “dwelt” in the countryside, it was in a place (or places) not frequently visited. Notice, then, what this fact implies about the speaker: he, somehow, has visited her dwelling place; he, somehow, has had the chance to know and appreciate her, and now he shares that privilege with the reader. The poem will imply that she was somehow a particularly intriguing person, but the poem will also imply that the speaker himself was capable of valuing a human being who might easily have been overlooked or ignored by others.