This is a great location to stay in Madrid. The apartment is in the middle of things; close to the metro, sights, food, entertainment. You can walk everywhere. No need for cab if you use the metro. If you fly in to Madrid get a multi day metro card at the airport and ride into town to the Sevilla station. Teresa is a wonderful host and the apartment is as offered.
Just one word of advice, the bedroom is on the street side of the apartment and some nights it can get rowdy. Bring ear plugs if you are a light sleeper. I would not let this keep me from renting Teresa's apartment again.