I stayed at Carmen's apartment with my girlfriend for a week.
We enjoyed staying there very much. The apartment is private, clean, modern, has all the amenities you need and the host is great. The apartment includes an Italian self service breakfast and Carmen even made us a tasty Tart one day :-)
Carmen is a great host, very kind, generous and will make an effort to make sure you are comfortable.
The apartment is in San Lorenzo outside of city center and tourist area, 20-30 minutes walk from Rome Termini and the Colosseum with near by public transport. The area has great and cheap restaurants.
If in Rome again we wouldn't hesitate staying there again.