The 14-year-old ate at a pizzeria in the Gianicolense district and went into shock approximately 15 minutes after her family returned to their hotel.
She was taken to the San Camillo hospital, where she passed away.
Her father was also admitted at the same time with heart issues.
The Guardian reports that the incident happened last Thursday (October 24) and was the first meal the family had eaten after arriving in the capital city.
It is understood that they had booked tours at the Colosseum and Vatican Museums during their holiday.
It is not yet known if the restaurant they dined at was aware of the teenager’s peanut allergy.
An FCDO (Foreign, Commonwealth and Development Office) spokesperson said: "We are supporting the family of a British child who has died in Italy and we are in contact with the local authorities."