I definitely recommend staying at Clara's place !
The apartment is spacious, luminous and very comfortable. It is located in an alley and therefore very quiet, far from the sounds of the street.
It is in the centre of Lisbon, although not in the touristic areas. You can walk to downtown in 15-20 minutes (walking back to the apartment takes longer because uphill ! but it is only 10-15 minutes from Intendente metro station).
Clara is a very good host and available when we had questions.