Edgar Allan Poe wrote "Annabel Lee" in 1849 to memorialize his wife, Virgina, after her death. (On a side note, Poe's most popular poem during his lifetime, "The Raven," was written during his wife's five year long battle with tuberculosis.) "Annabel Lee" was written so Poe could move on from Virginia's death. For five years Edgar Allan Poe had stayed by his wife's side while she suffered horribly from her disease. This bedside vigil caused Poe much pain and turmoil. It has been stated that the poem was written in order for Poe to be able to move on after Virginia's death (soon courting both Sarah Helen Whitmanand Sarah Elmira Royster).
That said, the girl in the poem lives to do one thing and one thing only: love the speaker of the poem and be loved by the speaker in return (historically denoted as Poe himself).
And this maiden she lived with no other thought
Than to love and be loved by me.