Long story short, we had the most wonderful stay.

The apartment is located in a great neighborhood, it was very clean and comfortable. Penny made us feel welcome, she even left us a coffee cake she had baked just before (it was warm when we arrived! and delicious, it goes without saying :)).
The apartment is more (and better) equipped than most high end hotels (towels, tea bags, coffee pods, bottled water, lots of guide books on DC, bathrobes, etc.)
I was sleeping on the sofa bed, it's very comfy.

I highly recommend this apartment!