What might I put on a timeline of Mary Shelley's life?

Though I cannot draw up a timeline for you, I am happy to share some important events of Mary Shelley's life in chronological order.

Mary Wollstonecraft Shelley was born on the 30th of August, 1797, in London, England. Her parents were William Godwin, a political philosopher, and Mary Wollstonecraft, a feminist writer who died shortly after giving birth. In 1801, Shelley's father married a neighbor woman, who Shelley would never really get along with. 

In 1814, Mary fell in love with one of her father's (already married) students-- Percy Shelley. The two ran away together to Europe, where they traveled for some time. In 1815, when they returned to England, Mary was pregnant with a daughter who would not survive more than a few days. Mary and Percy traveled often because they were looked down upon for adultery in England. In the summer of 1816, while staying in Switzerland, Mary begins work on her most famous novel, Frankenstein. Later that year, Percy Shelley's wife commits suicide, freeing the couple to be married.

In 1818, Frankenstein is published anonymously, and the Shelleys move to Italy. While in Italy, she conceives and gives birth to three more children, only one of whom would survive. This was Percy Florence, born in November of 1819.

In 1822, Shelley's husband Percy drowns in the Gulf of Spezia. After the tragedies of Italy, Mary and her son Percy return to England in 1823. Mary devoted herself to her son's upbringing and her writing, publishing numerous works until she died of brain cancer in 1851. Some of these texts include The Last Man (1826,) Falkner (1837,) and Rambles in Germany and Italy (the final format of which was published in 1844.)

For a thoroughly detailed chronology of Mary Shelley's life, please consult this resource from the University of Maryland.