My wife, two daughters (12 & 17), and I stayed in Lena's apartment for two weeks. Lena was very accommodating, very responsive and provided many suggestions for bakeries, grocery stores, etc. The location was great for us - a metro station right outside the door and walking distance to many of the areas we frequented (e.g., Les Halles, Latin Quarter, and beyond); the neighborhood seemed very safe. The apartment itself accommodated the four of us surprisingly well - even with only one bathroom (which looked like it had been recently renovated). It was clean and comfortable - and Lena was nice enough to have set-up the sofa bed (where our daughters slept) before we arrived, which was perfect as they both needed to sleep by the time we got there. The kitchen was perfect for us to make a light breakfast each morning (along with goods from the bakeries that are a block from the apartment). We would definitely stay at this apartment again.
A couple of things to be aware of (please note, NONE of the following were issues for us, pointing them out as they may be for others): (1) The apartment is on the third floor of an older Parisian apartment building, which means the staircase is older, narrow, and has some odd turns. There is an elevator in a separate part of the building and we were able to use it to bring our luggage in and out, but you wouldn't be able to use this every time you come and go each day. So be prepared to get your steps in :-) (2) If you are not accustomed to having lived or stayed in a major city, you may find the street noise and subway a bit loud. For us it was 'white noise', but if you live in a quieter suburb you may want to pack ear plugs as a back-up.