While the response to this question depends somewhat upon the reader's interpretation of characters, the changes that occur in Mr. and Mrs. Gunliffe are very natural and realistic. Since their son considers Mally "a vixen" and she is known for being rather untamed and certainly against Barty's gathering seaweed from what she feels is her cove, they would naturally be angered and frightened and believe that Mally had done harm to their son when they first see him pale and wounded in the head, seemingly dead. However, there are few parents who would not change their hearts and be grateful after learning that Mally has saved their son's life. The father, then, says, "I'll never forget it on her--never," and the mother tells Mally, "...thou art my child now, and I shall think of thee so." The Gunliffes' changes, therefore, seem to be the most realistic.
On the other hand, the transformation in Mally seems rather mystic. For, in the beginning Mally holds malice in her heart for not only the "thieving" Barty, but also for his father who "wanted to buy her weed at his own price." But, as the rescued Barty lies prone on the rock, Mally supposedly looks at him and "knew that he was beautiful. What would she not give that he might live?" Later, when Barty kisses her hand in gratitude, Mally thinks he is "like an angel" whereas, just prior to this, Mally recalls that Barty "was her enemy." Therefore, this sudden change of loving Barty seems unrealistic and more the stuff of Irish tales.