Aygen is the best host you can ask for and I am saying this from experince, having tried multiple listings in the US and Mexico. She is great in communication and she would be there for you if you need anything. She was very quick in getting back to whenever I messaged her. She was very nice to even pay for my airport transfer taxi when I was struggling with my credit card. She told me not to worry and pay when you have cash and that saved me from a disaster on the first day of my trip.
Her aprtment was absoloutly clean (towels and bed sheets are snow white and super clean) with comfortable beds. It is locate in a lovely neighbourhood, 5-minute walk away from Galata Tower and the happening istiklal street. It is very close (less than 5-min walk) to Şişhane metro station (M2 line) and multiple bus stops also walking distance from Karaköy (Turyol) ferry terminal that could get you to many different destinations including Prince Islands.
The apartment is recently renovated so you can feel and see that everything looks new and fresh (she showed me the before/after picture and wow, the transformation was huge)
It was 5 of us and we stayed very comfortably at Aygen's place. You would need to plan and coordinate your shower time with the rest of your party (it only has one shower/bathroom) but other than that everything was perfect for us.
One thing to note about this apartment is that you will hear a lot of street noise from outside during the night but I bet this is not an issue specific to this apartemnt, any place (hotels or Airbnb) in this central part of Istanbul would be like this. Just a heads up to be ready for it and to bring your ear plugs or noise cancelling ear buds :)
There are many restaurants and cafe nearby and grocery stores also in case you want to cook a few meals.
I hope you choose Aygen's place and enjoy your stay as much as I did :)