Christina's place is perfectly placed within Barcelona. It's really close to all the Gaudi stuff (which you absolutely have to do), and close to very convenient public transport (pro tip- grab a T10 card).
The Gracia district was one of our favourite places to walk through in the evening. It's full of lovely little spots to eat and drink, and brimming with local life (would absolutely recommend La Cigale, a gin bar close by).
Rooms are nice and warm (during the winter). There's a little kitchen which is very handy to have.
Christina gives some great recommendations when you check in, and gives you a good 'lay of the land' so to speak. We had a mixed experience at La Fonda though - so your mileage may vary.
Basically, you can't go wrong with this place! Best of luck on your trip to Barcelona, and hope you have a great time!