So to keep it up with the positive reviews, Pelin's apartment is just great. It is exactly as shown in the pictures: cosy, bright, really clean... She really thought of every single detail to our stay perfect.
Unfortunately, my boyfriend and I didn't get to meet her in person but she and her partner gave us detailed instructions on how to get to the house where he was waiting for us to give us a tour around it. Pelin even contacted us during our stay to ask if we needed anything. She really cares!
The neighbourhood, Cihangir, in Beyoglu is fantastic as well. While being quite close to some of the main attractions, it is full of nice bars, restaurants and cafes where you can feel as a local. We did almost everything by walk!
To sum up, a very pleasant experience. If I ever go back to Istanbul (which I hope is soon), I would definitely stay at Pelin's again. Thanks so much for everything! :)