This part of the quest “La Cage au Fou” is one of the best (and most touching) parts of the entire game, in my humble opinion. Choosing to lift the curse and rescue Marlene de Trastamara is a wonderful thing. Everyone should do it when they play the game. The thought of someone not helping Marlene after experiencing such a stressful curse is beyond my comprehension.
Video: La Cage au Fou Part 3
The Witcher 3 Guide 