The best thing about Pauline's flat is the location in my opinion - you are 10mins walk from Gare du Nord; and 15-20 mins to Montmarte. There is a metro station 2-3mins away which connects you to a number of lines, including Line 1.
Pauline was also kind enough to allow me to check out a few hours later on a Sunday, which was much appreciated.
The bed could have been more comfortable - this would be the main thing I think she can improve.