We stayed in Sandra's place for a week and it was really nice. Despite the fact Sandra was abroad during our stay, she managed to leave all the instructions clear about getting her flat from the airport and how to open it. She was very helpful since the very beginning and was all the time asking us from the place she was if all was going on fine.
On the top of that, she gave us very interesting informations (she recommend us a great app to move around the whole city) and she let us to have coffee and tea and she left us some sweets as a check in present.
We strongly recommend anyone who look for a not short stay in Berlin the Sandra's flat not only for her detailed support but also for the good location (4 stops far from Alexanderplatz).