Sofia's flat was exactly as described and was absolutely perfect for our stay (2 friends staying for 4 nights). The area is quiet but only a short walk to Bairro Alto, which is a central location for nightlife, restaurants and meeting points, e.g. walking tours and bar crawls.
The flat has a good living space with a modern TV and some board games if you want to spend a night in! The kitchen, bedroom and bathroom are small but modern and have everything you need.
Sofia greeted us at the flat and told us everything we needed to know, plus there are maps and guides left by previous guests so that is handy. I even showed Sofia pictures of places I had been before but couldn't remember where they were and she knew exactly where they were and how to get there! Also, the cinnamon liqueur that Sofia offered as a welcome drink is absolutely delicious! She recommends a Portuguese restaurant at the top of the road and we would highly recommend going, it's a local diner that serves grilled fresh fish, we went twice because we loved it.
We absolutely loved our stay in Lisbon, it's a great city for young people and a beautiful place to walk around, plus staying at Sofia's flat made us feel very comfortable, so we did not want to leave :)