I can only repeat what others have said about the interior design and the private room: very tasteful, clean and calm. The bright windows were particularly nice in that hot period. Bastille area is not without reasons my favourite place for a stay in Paris;a lot of nice and relatively affordable restaurants, the alligre market and not to pretentious .
What I particularly want to point out in my review is Nina's hospitality. When I came home from a long working day in that hot weather she welcomed me with a cold homemade soup, she would also let me try cheese with truffle and I was free to have some of her food. Nina is also a wonderful person to have a chat with. The arrangement of the language, arriving/departing hours were very easy to organise with her. Thank you for that.
So all in all, I highly recommend a stay at Nina's flat!