I stayed with my family at Sabrina's place for 3 nights. As we had limited time to visit Florence we wanted to be as close to the city center as possible, and let me tell you: we were LITERALLY just like 3 blocks away from Duomo SMF and within walking distance to everything. Location wise it has been a dream. At first you get worried because there are two bars right beneath you, but you'll hear absolutely nothing inside the apartment (believe me we have a very light sleep). The place feels super "homey", it has a modern heating/cooling system and the beds are suuuper comfy.
Communication with Sabrina has been exellent and I'd recommend this apartment to anyone visiting the city. I'll even recommend it to my own friends. Do not hesitate.