She died almost as soon as they arrived.

According to Newman Ivey White,[xii] Mary, in the unreasoning agony of her grief, blamed Shelley for the child's death and for a time felt toward him an extreme physical antagonism which subsided into apathy and spiritual alienation.

Mary's black moods made her difficult to live with, and Shelley himself fell into deep dejection.

He expressed his sense of their estrangement in some of the lyrics of 1818--"all my saddest poems." In one fragment of verse, for example, he lamented that Mary had left him "in this dreary world alone." Thy form is here indeed--a lovely one-- But thou art fled, gone down the dreary road, That leads to Sorrow's most obscure abode.
Thou sittest on the hearth of pale despair, Where For thine own sake I cannot follow thee.
Professor White believed that Shelley recorded this estrangement only "in veiled terms" in _Julian and Maddalo_ or in poems that he did not show to Mary, and that Mary acknowledged it only after Shelley's death, in her poem "The Choice" and in her editorial notes on his poems of that year.

But this unpublished story, written after the death of their other child William, certainly contains, though also in veiled terms, Mary's immediate recognition and remorse.