The place is very charming, and the location is excellent. It has an authentic traditional Colonial Mexican flavor, without feeling staged. "La Casita" is very pretty, neat and quiet. Property is very well maintained and there are lots of plants, which give it a really nice feel.
Metro station is 5 minutes away on foot, and other public transportation is available outside the Metro station as well (taxis, "peseros" and buses). If you hop on a "pesero", you´ll be in Coyoacán in 15 minutes. If you ride Metro, you´ll be in Mexico City´s Centro Histórico in less than 30 minutes ´–and it´s so inexpensive!–.
Luz was quick to respond from the very beginning and she's a great host. She's very nice, helpful and kind.
The only minor thing was having to share the little courtyard with the long-stay guests from the apartment next door, who had two dogs (although there was a gate to keep them from running loose and it was very clean). This was a non-issue; they were nice people, and the dogs were well behaved and cute, but it would have been better if we had been able to enjoy the courtyard in full.
Regardless, when we go back to Mexico City, we will definitely stay there again!