I had a very pleasant stay at Sandra's. Her friend Vanessa welcomed me and was very helpful, I appreciated her tips and advice on the neighborhood. The apartment is very well located, in Alfama, even if some taxi drivers struggle a lot to reach the address (I recommend walking a bit to catch a taxi or a Uber, otherwise they won't find you and you will wait endlessly ^^).
The neighborhood is totally safe and friendly, the street is full of little restaurants where you can experience "fado" the proper way.
The apartment is clean and very spacious, with a patio that must be great in the summer. If you plan on visiting in the winter, as I did, be aware that there is no heating in the apartment, and it makes it really cold. The wifi is slow and there's not much light during the day. I recommend this place if you're looking for a safe and pleasant place to sleep after a long day of visiting Lisbon, in a friendly neighborhood.