Location, Location, Location: That's #1 criteria and this place fits the bill.
Second, quaint-ness or chic-ness of the place. Again this place fits the bill.
The whole house is fantastic. The kitchen (which we rarely got to use given the choices of local restaurants), is awesome. Everything is/was perfect for our family. Our 15 year Son said that himself - he would prefer this to hotels or any other.
Its 10 mts walk to Vatican
Its right in the Trastevere area with Saint Maria Basilica
Its 15-20 minutes walk across the Tiber river with so many good restaurants, shopping, Pantheon, Other old ruins, Spanish steps etc etc. Too many to name here.

If we do go back to Rome, we will certainly reach out to Sara and try to reserve the same place.

If i were to suggest - only 2 things
1) The master bedroom should find a way to get sunlight (Hard).
2) The Wifi access point should be improved or kept in a more central place in the house. Other than 3 feet from where its kept, could not get any signal.

The street where the house is, while it looks a little rundown (most streets in Rome might), its small and narrow and no easy local parking. More importantly to get to the apartment - you have to climb some steps. Nothing wrong with the house, just be aware that to get to the place you have to climb 50+ steps to get to its gate and then another 30 steps to get into the apartment. So if you had a number of pieces of luggage (which we did), its a climb.