Errera was born in Venice on July 13, 1864 to Cesare, a Jew of Spanish origin, and to Luigia Fano, from Mantua, Italy.
After his death, the remaining family returned to Venice to live in the home of a paternal uncle who, despite having five children of his own, took in Rosa and her three siblings, Emilia (1866–1901), Carlo (1867-1936), and Anna Errera (1870-1940).
Over the next two years, her writings appeared in Il Piccolo Italiano, a Milanese weekly magazine edited by Aurelio Stoppoloni which proposed to "educate children by delighting them," but also urged them to live the "Italian spirit."
According to Paesano, her fictional works were written to replace "the spells of the fairy tale with the realism of family affections and domestic care.
Her illness required a change of scenery so she moved her residence from the busy center of Milan to a small villa on the city's outskirts, surrounded by greenery.
It had what has been described as a "somewhat artificial plot," featuring a meeting of well-known historical and artistic personalities (S. Francesco, Dante, Colombo, Leonardo da Vinci and Mazzini), who discussed the Italian national identity and revealed strong patriotic sentiments.
(Dante remains Errera's most widely available book, which, as of 2020, is still available in print with copies held by 34 WorldCat member libraries worldwide.
When she refused to pay tribute in her books to the new fascist regime, thousands of her printed works were destroyed, "sent to the pulp, never reprinted."
To survive during that time, Errera was saved from being deported thanks to her friend and sometime co-author Teresa Trento, "who kept her hidden in her home for over a year and a half.