I stayed in Helena's place for a month and I really enjoyed it, not only because she was very helpful and responsive.
The flat is big, clean and it has everything to let you feel a resident in Lisbon. A special mention for the internet connection that is really fast.
The location is amazing, Graca is one of the best place you could stay in Lisbon: full of life and really close to the city center. I prefered to avoid the underground but there is a metro station within walking distance.
In few words I totally recommend her place!