She was born in 1479 and would be about 24 years old when Leonardo painted her.
Her father was a Florentine Nobel Antonio Maria Di Noldo Gherardini.
She married in 1495 at the age of 16 to Francesco Di Bartolomeo Di Zanolsi del Giocondo who was twice a widower and 19 years her senior.
They became wealthy in the silk trade.
Leonard undertook for Francesco Zanobi del Giocondo the portrait of his wife Mona Lisa.
"Mona" is an honorific for a married woman. So the portrait is really a picture of Mrs. Giocondo. Kinda loses some of its mystique, eh?
There is a good biography out on the astounding Catarina Riario Sforza de Medici. It is by Elizabeth Lev entitled The Tigress of Forli.