Carmen is a very welcoming person, but even more important is:
Her little flat is tastefully furnished and very clean, really nothing is missing. It's perfectly located in walking distance to all the important sights in Madrid and to the Atocha Station, so perfect also for arrival and departure by train/to the airport.
Downstairs, right in front of the house is a nice little restaurant/bar where you can get a good breakfast or dinner for a very good price!
But if you prefer to cook for yourself the kitchen is very well equipped.