There are lots of good points about Maria's place. It's clean and well-equipped. The location is excellent. The metro is only five minutes' walk away and there's a small supermarket only a few minutes from the apartment that's open until 9 at night. And Maria has a warm personality and makes you feel welcome.
However, her flat can be noisy. It's under the flight path to Lisbon airport and the metro's Green Line runs beneath the building. More important, the room is next to the kitchen. This can be a problem if - as happened during my stay - one of Maria's family decides to prepare a meal at midnight. (Maria does not live in the flat; her two sons do.)
Noise apart, this is a good place to stay if you plan to visit Lisbon for a couple of days.