Answer and Explanation:
From reading the poem, we can see that people know a version of Aunt Imogen, the younger version of her, full of dreams and plans. However, the lack of coexistence and the loss of contact between the family, meant that they did not follow the changes that Aunt Imogen went through, which turned her into someone else, who no one knows anymore, just herself. Aunt Imogen's family knew her as someone happy and excited and they believe she remains that way, but inside herself, Aunt Imogen knows how sad, frustrated and lonely she feels. Only she knows this thought and only she knows herself completely.
In this case, the poem reinforces the idea that knowing someone does not mean knowing that person for real, as we do not have access to the deepest and most personal thoughts that transform a person completely. We only really know ourselves, because we can't get away from what we think.
We can see this in the lines:
<em>"Was there for only one month in the year,/ While she, the mother,—she was always there;/ And that was what made all the difference./ She knew it must be so, for Jane had once/ Expounded it to her so learnedly/ That she had looked away from the child’s eyes
/ And thought; and she had thought of many things."
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