Susana is an amazing host and the apartment is indeed very well located and within walking distance to the centre. We arrived by midnight to Porto and Susana had prepared a vegetable pie for us, so we could have a dinner. She also gave us suggestions for Porto and took us with her to a concert in a small local 'non- traditional' music studio.
I didn't use any public transportation as everything is indeed in walking distance. Would definitely stay there when coming back to Porto.