I stayed in Nina's studio flat for 5 weeks and had a great time and great experience. It really is the ideal of what an AirBnB accommodation and experience really should be. The flat is self contained with bathroom and kitchenette - it is spotlessly clean and has recently been renovated....so its very fresh and new, with nice clean design and feng shui (you have access to her adjoining apartment to do laundry, use the balcony / a full kitchen etc). It has a giant big window with great views of the street below. Nina was very hospitable and any queries, such as needing to use her washing machine, connecting to the WiFi etc, were dealt with promptly. Its in a really really nice area, situated next to Mariennenplatz, right in Kreuzberg but in a quiet area.
I can heartily recommend staying at Nina's if you are looking for a relaxing, quiet, safe, private place to stay