According to the excerpt, North Dakota symbolized bad experiences for Sofia. As she left North Dakota, she had no intentions of coming back, and this is most likely because of the bad experiences she had. It must have been so terrible living in North Dakota because she believed that her bird felt stifled.
She released her bird to have the freedom that was not available to it in North Dakota. She herself moved on to freedom in Montana. She believed that she would have a new beginning in Montana with better experiences.
