The apartment is very small, but cosy. Everything you need is there, from towels to iron, and you're in walking distance of the Gran Via, but also of Calle de Pez and some other nice streets and squares. The metro is very close by as well. So the location is really amazing!
We also got some tips from Isabel's husband when he came to bring the keys about where to go, which was really nice.
I only spoke to Isabel through AirBnB, I didn't get to meet her in person, but in that contact she was very nice and accommodating (we arrived very late at night, but she made sure we got the keys and were welcomed warmly).
Would definitely recommend staying here if you're in Madrid for a few days, it's a perfect base for exploring the city.