Maria's place was great! It is just as described in the pictures and we had an excellent stay there.
Check-in: Maria provided excellent instructions for us to get to the apartment from the airport, which made it very easy for us to get to location with no problems. Miguel (Maria's colleague) met us at the apartment for the check-in process. Miguel was very informative and thorough with the process and made sure to answer all of our questions with attractions and transportation before he left.

Location: The location is prime, in a safe and secured building with restaurants and supermarkets just downstairs. The location is 3-4 minutes walking away from the Paralel metro station which was very convenient.
The Apartment: The flat was just as described. It was very clean, and all the towels, linens, and cloths were washed and fresh. The private outdoor patio was a huge plus. The AC keeps the entire flat adequately cooled. The kitchen was well-equipped with any kitchenware we needed, though we admittedly did not cook while there (only reheated leftovers and used glassware).
The one very minor negative about the apartment is the orientation of the shower door and the door to the bathroom. You can't have both opened simultaneously, as one obstructs the other when both are open. As long as you coordinate its not that big of an issue.
Overall Maria's apartment is a tremendous value in a prime location and we would definitely recommend staying here for your trip to Barcelona!