We stayed for 4 nights and had a great time in Berlin.
Nicole's apartment is clean, well outfitted for all you need (shower,toilet,kitchen,sofa,television,radio,wi-fi).
Nicole and her family were lovely, and Nicole was eager to help us find out solving travel to/from the airport - gave us great pointers about a lot of useful stuff. She even ordered a taxi for us to the airport.
This apartment is perfectly located for Tegel airport, the taxi ride is around 10 minutes and it cost around 20 eur.
A short walk to the next train station was a big plus and the neighborhood is very calm and nice.
All in all, a very pleasant stay and I would definately stay here again :)