Tosi was born in Ferrara, Emilia-Romagna, on 11 July 1913. She married twice, but had no children. In 1946, she voted for Italy to become a republic; she moved to Genoa, Liguria, following the death of her first husband.

As a centenarian, Tosi was devoutly religious, attending church services regularly until the COVID-19 pandemic, during which she would watch the services on the television. She is also a football fan, has a strict daily routine, and has never smoked.

At the age of 105, Tosi moved into a nursing home in Genoa. As of 2023, she is among the top 20 oldest residents of Italy.