We stayed in Monica's apartment for three nights. We were greeted by Ambra, Monica's sister and she was utterly delightful. Ambra offered restaurant recommendations and a quick overview of the amenities close by and organised our taxi to the airport on departure.
The apartment was a 5-10 min walk from Piazza Navona and a 10-15 min walk from St Peter's Basillica (if you take the right route!). The surrounding area is packed with great local restaurants far enough away from Piazza Navona to ensure you are getting a truly Roman experience rather than a tourist experience.
The apartment was on the fourth floor (it's a walk-up, no lift, but even my 80 year old mother was able to manage, so don't let this put you off) and had an amazing little terrace, it is unfortunate that we didn't utilise it as much as I would have like to (too many things to see and do in Rome).