What does the transformation of old woman to a young lady symbolize in the play Cathleen ni Houlihan?

At the very end of the play, Peter and Bridget ask their youngest son, Patrick, if he saw an old woman coming down the road when he got back home. He tells them that he only saw a young woman who was walking like a queen. In this moment, we realize that the withered old Cathleen ni Houlihan has transformed into a beautiful young woman, like in a fairy tale. This transformation is symbolic, representing the fact that Michael's devotion to the Irish cause has revitalized Cathleen and turned her into a young beauty.