I stayed at Maria's place for a week while I visited family and the city. Maria was a great host, very friendly and very helpful. The place was great, and way beyond my expectations. It is akin to a mini studio, but very confortable, with a confortable twin bed, a mini kitchen (with a mini fridge, stove, etc), a desk for work, a nice bathroom, and a very espacios closet. It has a private entrance, which is great for privacy, but it is next to Maria's main apartment, should you want to contact her in person.
The place is in one of the best locations I have been in Madrid, close to everything, very central, but not too crowded or congested. It 5 minutes to Nuevos Ministerios, a main T stop (for Metro/Cercanias) which makes traveling the city a breeze.
I would absolutely recommend Maria's place, and plan to visit again hopefully very soon.