Rosanna and her children fled to Venice where she and her eldest son, Francesco, used Perception filters to appear human. They had come to Venice because of their marine nature and to exploit the fear of the plague. They set up a "school" under her management. It gained fame in the city as a plague-free haven and became fashionable.
Once the girls were in the schools, their blood would be replaced with that of the Saturnyns, and they would be transformed into females of the species, ready to help drown Venice and form a new race with the other male survivors. In 1580, Amy Pond and Rory Williams attempted to infiltrate the school with the aid of psychic paper, although Rossana was able to see through it and imprisoned Amy.
After escaped with Isabella's aid, Rosanna had her devoured by her sons before sending the female converts to eliminate the Doctor and his companions. This ultimately led to her race's end when Guido sacrificed himself to destroy the converts. With nothing left to lose, Rosanna activated the final phase of her plan, creating a storm of boiling rain to sink Venice. However, the Eleventh Doctor disabled her machinery and her son Francesco was killed by Amy and Rory, leaving her plans in tatters. With no hope of rebuilding her species and her perception filter broken, Rosanna was stuck in human form. She threw herself into the canal and was devoured by her children because they could not recognise her and thought she was a meal. (TV: The Vampires of Venice)