Why does Munro end "To Reach Japan" with Katy pulling away from her mother?

At the end of To Reach Japan, the sentence portraying one of the girls' "pulling away" actually leaves its grammatical subject ambiguous. That is, it isn't explicit whether Katy or Greta is the one who recoils from the other. This grammatical ambiguity suggests a kind of duality or opposition in the way mother and daughter are related in the story.
Reading it in one way, it can be said that Greta repelled herself from Katy in a selfish impulse tied to her desire to break from a past which includes Katy. Conversely, Katy might have broken from her mother's grasp because she rationalizes her mother's behavior as negligent. Katy also could have pulled away out of a desperate yearning to fashion her own future without keeping Greta as a model. All of these meanings are valid interpretations of the text's deliberately open-ended conclusion.
Significantly, after the "pulling away," the characters take hold of each other again, which can be read doubly as an act of resignation and of love.