Our stay in apartment was just perfect. Kirsten is a great host, we didn't have any problem with communication at all.
Neighborhood is vary safe, residential but still full with shops, markets...
The main metro line U2 is 5 min walking from the apartment. To the center is about 20-30 min (Berlin is really big city).
Very, very clean, bright, warm and cosy apartment. Equipped with everything. We were four of us and it was comfortable. Its hard to find nice app in Berlin with two bedrooms, but still with good price.
I recommend Kirsten's place to everybody.
Hope see you again!