Isabel's apartment is marvelously located: about 10mns walking of everything. From there, you'll be able to stroll to the cathedral, the Alcazar, Las Setas very easily. Other burroughs aren't very far either so Triana, Santa Cruz, etc. will be easy to access.
The place is quiet and the apartment was very clean and had everything you need inside. There's a supermarket few hundred meters away if you want to cook at home.
Indications from Isabel were very precise and her friend was very kind and guided us to the apartment.
I would definitly recommand Isabel's place if you want to stay a few days in Sevilla.