Who is Lucy in "She Dwelt Among the Untrodden Ways"?

This poem describes the appearance of an unknown girl named Lucy and mourns her death. Many believe that Lucy is the poet's sister Dorothy. The poet may have lamented Dorothy's future death. Many believe that Lucy is Peggy Hutchinson or Margaret, whom the poet once loved. She died in 1976. Peggy was the sister of Wordsworth's wife. Many people think that Lucy is a mysterious character. Many people think that Lucy is a fictional character.