Searching for Isabel Godin

Celia Wakefield, a retired travel writer "with no more pressing responsibilities," first encounters Isabel Godin in a library in Cuenca, Ecuador. There in a book of 18th-century prints is a portrait of a small woman with delicate features, aristocratic clothing, and a level, serious stare. The picture is titled "Madame Isabel Godin des Odonais, heroine of a terrible journey on the River Amazon." What could that journey have been? Why did she take it?
It so happens that Madame Isabel is linked to the very subject that has brought Wakefield to the library: the French Geodesic Mission of 1735-1742, dispatched to Peru to determine the exact shape of the earth. Led by the colorful Charles-Marie de La Condamine, "the Humboldt of the 18th century," seven scientists investigated icy volcanoes and the steaming jungle, and it seems that one of them, Jean Godin, fell in love with a lovely girl from Riobamba named Isabel Grandmaison.
Isabel and Jean were married, and when the other scientists went home Jean stayed behind. He planned to return to France with his wife later, but circumstances compel him to go ahead. Eventually Isabel sets off to descend the Amazon to rendezvous with her husband. Hers is a tragic voyage of unbelievable suffering, the stuff of great fiction, but true.