Almost Invincible is the story of Mary Shelley (author of Frankenstein) and how her life was coloured by the poisonous influence of a step-sister, Claire. Mary died in February 1851. This is the letter Claire sent to Mary’s son Percy, after she heard of the tragedy, and it illustrates her character well.
Source: The Letters of Mary Wollstonecraft Shelley Vol III Ed. Betty T Bennet, John Hopkins University press