I think that Flaubert is able to bring about a fairly realistic portrayal of his "saint," Felicite, in that he does not allow her religious zeal to escape the difficulties faced in daily life.  This is what makes her narrative so realistic.  She must encounter death on a sadly regular basis with the death of Virginie and the death of her nephew in Cuba.  Her religious faith does not prevent her from honoring Virginie's body and cleaning her grave, realistic details that reflect Felicite's sense of honor and dignity and make her more receptive to the reader.  When LouLou flies away, Felicite becomes sick in trying to find the bird.  Her saintly status does not prevent her from dealing with illness.  At the same time, Flaubert shows that Felicite's saintliness is a challenge to social situations and does not seek to evade the difficulty she faces in dealing with them.  Helping the sick and the displaced, and those who have sinned are all part of what she does and not elements from which Flaubert shies.  In this, Felicite is shown as a saint, and one that must deal with the daily challenges of being in the world.  It is here where Felicite becomes more receptive to the reader and to Flaubert, as well.