Could not find a more centralized location in Rome. Easy walk to the Vatican. Slightly longer, but, we also walked to the colosseum. Pantheon is a short stroll away.
To get to the apartment, we took the "Sit bus shuttle" (look up on google) from the airport to the Vatican City stop for 6 euros and walked from there. Reserve ahead of time and you will skip a long line at the airport. Super, super convenient.
Antonella is incredibly sweet and will try to make your stay as nice as she can.