Mary Shelley was the writer famous in her own right for the creation of
Frankenstein, and was the wife of the poet
Percy Bysshe Shelley and the daughter of the feminist
Mary Wollstonecraft and the radical philosopher
William Godwin.
She was born in 1797; her mother died from it. Later Godwin married a Mrs Clairmont, who had a daughter Jane (1798-1879) by her first marriage. Jane was usually called Claire.
Percy Shelley was poet, eccentric, atheist, vegetarian, democratic, and socialist; he had read works by the likes of Godwin, and been expelled from university for atheism. In 1811 he had eloped to Scotland with 16-year-old Harriet Westbrook. They had two children, a nomadic life, and free love, but the marriage collapsed in 1814. Despite the fact that Harriet was suicidal, Shelley eloped with both stepsisters, 16-year-old Mary Godwin and 15-year-old Claire Clairmont.
They travelled over the Continent, then back to England, and to Europe again. Claire had a daughter Allegra by their friend Lord Byron. It was in a castle overlooking Lake Geneva in 1816 that the friends and lovers told each other ghost stories; the most lasting legacy of that was Mary's novel Frankenstein, or the Modern Prometheus, published in 1818.
Harriet Shelley killed herself in 1816 and Mary and Percy were immediately married, though the trio with Claire remained until the end. Of their children only one, called Percy, survived long. The poet was drowned off Italy in 1822, and Mary returned to England the following year as his literary trustee, arranging and prefacing his poems, essays, and letters
She wrote numerous other works of various kinds - novels including Valperga (1823), Lodore (1835), and Falkner (1837) - travels, biographies, stories - often of Gothic style, with a recurring element of what can be called science fiction. She died in 1851. Apart from Frankenstein, on which her literary fame rests, I've only read (and only seen) one other work: her futuristic novel The Last Man (1826). See that node.