Lenore is the supposed "Lost love" of the narrator. Since most of the women in Edgar's life have been lost due to tuberculosis, we can only assume that she passed due to the illness.
Pretty much...Poe never explained her death in the poem, and it obviously took place before the events of the Raven, but there is nothing there to say how or why.
I wonder if he wasn't just looking for a rhyme with "nevermore"
