Astrid Guarini died after being bitten in the neck by the family pet, a five-year-old German Shepherd named Cloe, Il Messaggero Veneto reported on Monday.
The toddler had been playing in her cousin's garden in the village of San Martino al Tagliamento when the accident took place.
Police are currently investigating how the attack happened based chiefly on the account of Guarini's eight-year-old cousin, the only witness.
The children were reportedly left alone with the family dog, who had never shown signs of aggression, and may have been been feeding him when he bit the toddler.
Guarini's mother, Mara Menotto, rushed into the garden when she heard her niece's screams.
Emergency services arrived by helicopter and ambulance, taking the toddler by road to Pordenone hospital around 20km away.
Medics tried in vain for two hours to save the girl, Il Messaggero Veneto said.
The dog was seized by the authorities and taken to a kennel in Villotta while the investigation continues.