We didn't get to meet Arantxa nor her sister, but it wasn't even necessary. They contacted us both (phone and messages) when we arrived to check if we are fine.
Apartmant is nice and clean and has everything you need for a pleasant stay. It's on the 3rd floor, but there is an elevator. The location of the apartment is the best possible. Everything is just there. It is a little bit noisy in the evening as well, but that's the price you have to "pay" if you want to be centrally located.
There's so many to see in Madrid, so we have decided to go back to Madrid soon and we will definitely stay at Arantxa's place again.