I stayed at Sandra's apartment for 10 weeks while studying in Barcelona. It was a great place to stay as a female alone in Barcelona for the first time.
Transport: Excellent, right next to the Fontana metro station and within easy walking distance of the Gracia FGC. I generally walked everywhere as the main tourist sites are not far. Gran de Gracia (the attached street) turns into Passeig de Gracia (main tourist strip) after a 10 minute walk.
Convenience: The street parallel to the one the apartment is on (d'Asturies) is great for all food shopping including lots of organic produce. I highly recommend the bakery "Mistral" on the corner - you won't miss it as there's always a line. Gracia also has some of the best restaurants and cocktail bars in Barcelona.
Apartment: The apartment is very spacious and fine for two people for a few weeks. Note that it is older, but the kitchen and bathroom have been renovated. It's also very safe (important for a single female), with a double deadbolt on the front door and shutters. The kitchen has all the utensils you need if you prefer to cook at home.
Communication: Sandra is a fantastic host and always responded immediately. She even organised for the cleaner to come a few times during my stay.