After 2 days trying to join Katrin by Airbnb, mail, whatsapp... I finally got an answer at 10:00 PM the day before our arrival!
The apartment is very clean and same than pics. Just some details need to be finish as it is brand-new (electricity cables, kitchen ventilation)
You will not see Katrin during your stay. She lets the keys in a safe box. It is not an apartment you can expect on this site as nobody ever lives there. It was only thinking for rent. Katrin has several apartments for business in Berlin but she is not an host! She did not even answer to my questions on how to get to the apartment from the airport. To sum up, it is a hotel without a reception more than an Airbnb flat.