Costanza's place is in the perfect location-- very close to Campo di Fiori and Piazza Navona, just over the Ponte Sisto from Trastevere, and in walking distance to the Vatican, the Pantheon, and Trevi Fountain. The apartment is cozy / on the small side (a studio), but a comfortable size for two adults with not too many bags. It was quiet and felt safe. Our only complaint is that the air conditioning was not cold enough, granted we were there during the "Lucifer heat wave" in Rome.
Costanza was extremely responsive, there when we were ready to check in, and was able to schedule a car service for us to get to the airport at 4:00am. I would highly recommend her apartment!