I stayed for a month. Cintia was an amazing host! Like others have said, she thought of everything. The apartment is spacious and clean, she provides subway/bus cards, has a guidebook filled with restaurant suggestions and maps, and even had a basket of snacks and water upon arrival. She gave me a tour and was available for any additional questions.
The apartment is a block away from the San Juan subte and a 15 minute walk away from Mercado San Telmo. Puerto Madero and La Boca are also walking distance, though much farther than San Telmo.
It's a great apartment, Cintia is amazing, and will stay again when I return.