We stayed in Mabel's apartment for a little over a week in late April/early May 2014. Mabel and her family were lovely and very accommodating, even going as far as to lend us some money when we first arrived because we hadn't had a chance to change any currency yet. They also printed our ferry tickets for us last minute! They quickly responded to any messages we sent and were helpful with local information and tips.
The apartment was very well located in Palermo Hollywood, close to supermarkets, cafes, restaurants, a heladeria (just across the road!) and a block from Ministro Carranza subte station.
The apartment was as described, with a separate bedroom, full bathroom (with plenty of hot water and good water pressure), excellent WIFI and a reasonably well equipped kitchen (although previous guests had left some of the crockery, glasses and pots a bit grubby).
A couple of minor downsides, the bed was a bit smaller than we'd expected from the description and the bedroom was right on the street so there was quite a lot of noise from traffic and people walking past the window. Also, one of the neighbours must be a smoker, because we would regularly smell cigarette smoke wafting through the apartment.
Aside from those small things, we had a great stay and would recommend the apartment to others visting Buenos Aires.