We were 3 friends, staying 3 nights in Carla's appartment and we liked it a lot. The flat is very close to the metro and the subway, but we did almost everything by walking as it's close to the main districts of Lisboa. Carla wasn't there to welcome us but the communication was very easy, and she made sure everything was ok.
We had a pleasant stay, the only thing is that the building is old so you can hear any noise coming from the stairs. And there were some building works from early in the morning (but not during the weekend).
But I would recommend Carla's flat anyway!