My mom and I stayed in Marina's apartment for four nights and had a wonderful time. The apartment was literally steps from the Capitol and Library of Congress. Getting around on the Metro was easy and the Capitol South stop was a five minute stroll down D St. (less than two blocks!)
We arrived early in the morning and Marina was kind enough to meet us and let us stow our luggage in the foyer until we could officially check in. Marina has a binder in the apartment with maps and brochures, and was also very helpful the first day with tips on getting around the city. The keyless entry made coming and going very simple.
I recommend renting this apartment with someone you don't mind sharing a bed with, as the couch is not very comfortable. Since I was with my mom, this was not really a problem. The bed is VERY comfortable and soft with ample blankets and pillows. The kitchen and bathroom were newly renovated and lovely. There were plenty of towels and washcloths, and Marina also provides shampoo, conditioner, and body wash if you don't want to bring your own. The kitchen is stocked with cups, plates, silverware, coffee maker, and french press, as well as pots and pans for a little cooking if you want. We were well equipped to make a little breakfast, however someone trying to make a big dinner may be left wanting in terms of cookware and utensils.
Overall, we had a great time. The apartment was lovely, the host kind and accommodating. I would DEFINITELY stay there again if I was going to visit DC.