Arcelia is a very generous and responsive host. I give her an A grade. However, the space isn't for everyone depending on your tolerance for noise, how long you are staying, and what you want to be close to.
The other reviews seem glowingly positive so I'll break from the norm to highlight some things people could potentially have issue with:
The loft is on the first floor and faces the street. While it is not the busiest street in cdmx, there is a fair amount of noise from about 7am to 11pm intermittently. This can be difficult if you're trying to concentrate and don't want to have headphones in all the time. The building has a few dogs that are corralled during the day in the garage which you have to pass through to get in and out. They can be loud at times when other dogs pass by on the street (which is very common). If you don't like dogs at all, don't stay here. You will hear music being played during the day from the neighbors. Nothing abrasive.
Finally, during my stay the mattress provided was extremely hard. Upon rising, I felt like I had slept on a camping mattress in the wilderness...not a bed. Having stayed at other places in the city, it is certainly outside the norm.