The apartment is lovely, very spacious for two and comes with all the basic amenities you'll need.
I did not get to meet Marcia but she was very responsive and helpful over email / message. No problem in communicating in English.
Excellent location right in the middle of the historic centre!
Just one thing to note if you are a light sleeper - the apartment is on the top floor and you can hear the steps if there are people walking on the roof top. Also, given its prime location, it can get a little noisy if you leave the windows open.
Overall great stay and I would recommend this apartment if you're visiting Mexico city!