Fanny 's half - sister Mary grew up to write Frankenstein and married Percy Bysshe Shelley who composed a poem on Fanny 's death .
Percy Bysshe Shelley is a leading Romantic poet .
Fanny 's half - sister Mary grew up to write Frankenstein and married Percy Bysshe Shelley , a leading Romantic poet , who composed a poem on Fanny 's death .