Helena's apartment is a wonderful place and I would highly recommend it. The neighborhood is quite and charming. The views are amazing. Helena is a very warm host and was able to secure us a reservation on our first night in Lisbon (at Tasca de Esquana, a short walk from the apartment -- highly recommended). We would definitely stay here again.
Keep in mind that the apartment is on the 5th floor and the elevator only goes to the 3rd floor. The entrance to the elevator is one flight up from the street and is easy to walk past.