Sibel's place was extremely nice - large, spacious, sunny, with great furniture and amenities. As others have mentioned, there is a bit of noise coming from the port across the street, so I would recommend taking a pair of earplugs with you for the night. That said, the apartment is one of the best I've seen in Istanbul. It also has an elevator (and no steps required to access the elevator), which was very important to us.
Sibel herself was very communicative and quickly responded to all our questions at any time.
Highly recommend this place.