Isabella was the daughter of Guido, in Venice. She was sent to Rosanna Calvierri's school to become a bride for Rosanna's sons, which she was unaware of. She was put through the transformation, but was not as far through as the other girls around her.
When Amy went under cover as one to open the trap door for the Doctor, Rory Williams and Guido, she met Isabella on the way there. When the Doctor and the crew were trapped, Isabella showed them the way out but couldn't make it out because the sun burnt her skin - despite not being a full Saturnynian yet. Later, Rosanna deemed her a traitor, and punished her by pushing her into the canal. Thinking that the aim of this was to drown her, Isabella swam for a brief moment. Seconds later, however, she was pulled under by Rosanna's children, and was devoured.
Later, the Doctor talked about the subject of her death to Rosanna. He was greatly angered, because Rosanna did not know her real name, thus killing her without even knowing her. (DW: The Vampires of Venice)