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.
Tosi has been reported by several Italian news outlets since her 107th birthday in 2020.