At the beginning of the story, Grete is committed to taking care of Gregor. She feels compassion for him, and represents the only human contact that Gregor has.
However, as time goes by, Grete assumes a new role in the family. She starts earning money and taking care of the house. These new responsibilities make her change from a girl into a woman. At the same time, this tranformation diminishes the pity she feels for Gregor. She comes to think of him as a burden and unwanted duty, and eventually decides they need to get rid of him.