Lucia is a great host: not only is she very kind, but also VERY knowledgeable about Florence and Tuscany: if you are staying at her place, I would totally recommend that you ask her advice! The location is not in the very heart of the city, but in a quiet residential area approximately 20 minutes away (by walk), or a few minutes by train. There are local supermarkets nearby, which is a plus.
With regards to the flat, it is very pretty and absolutely spotless. The room is lovely, quite spacious and with a lovely terrace.
Being a host myself, I had read many reviews before booking Lucia's place, and you can book with confidence and ignore the very few negative ones, because they were obviously written by people that don't understand Airbnb: you are staying at Lucia's own house, so of course you need to be respectful of her place, and not treat it like it's a hotel!
The only thing you need to be aware of, is that one of Lucia's (lovely) cats can actually open doors (!), and he tries to do so when you're inside by jumping against the handle, even early in the morning. One day we came back and he was actually sleeping on the bed. The reason I mention this is that I think that "being ok" with cats might not be good enough to make you feel comfortable in the flat. You must really like cats, in which case you will enjoy Lucia's place probably even more.