Edna's flashbacks illustrate the fact that Edna has always felt different from the people that surround her. In chapter 7 the narrator says that "even as a child she had lived her own small life within herself." Edna's feelings and actions in the present time of the novel are not completely new feelings for her. She is not simply unhappy with her marriage or her role as wife and mother. She has felt a sense of disconnection between herself and the expectations of society and the traditional roles she was supposed to uphold. She marries Leonce "on accident" because she was flattered by him and his Catholicism irritated her father and sister. She has a benevolent disregard for her children. In the last pages of the novel, as she is wandering out to sea, the rememebers an earlier night of swimming, and that reminds her of a feeling from her childhood.
She went on and on. She remembered the night she swam far out, and recalled the terror that seized her at the fear of being unable to regain the shore. She did not look back now, but went on and on, thinking of the blue-grass meadow that she had traversed when a little child, believing that it had no beginning and no end.
The flashbacks provide insights into this woman who leaves what could be seen as a very nice life, and in the end, realizing she can't have everything she wants or that she isn't strong enough to maintain herself in this life, decides to end it all.
The flashbacks to Edna Pontellier's past primarily function as character development. We come to understand Edna's nature, her inclination to get lost in dream, in fantasy. Also, these flashbacks function to drive the plot forward, to understand more the present moment happenings and why she may be making the choices she does. Her history is established in these flashbacks, further clarifying for the reader Edna's relationship to other characters and how the past affects the present.