This is a fascinating question regarding this excellent novel concerning the breaking away from contemporary gender roles of a woman who experiences an "awakening" about herself. Certainly Edna says to her friend, Adele, that she would never sacrifice herself for her children. At the end of the novel, when she does sacrifice herself by committing suicide, it is important to ask who she does it for.
Although much debate exists over the meaning of her suicide, I personally think it can be interpreted as a feat showing the courage and determination of Edna. It demonstrates her understanding that a woman who is in search of independence as she is really has no way of achieving what she wants in a society that is so eager to reinforce and maintain gender roles.
As Edna goes down to the beach she is thinking hard about her situation, about the bleak future that awaits her:
The children appeared before her like antagonists who had overcome her; who had overpowered and sought to drag her into the soul's slavery for the rest of her days. But she knew a way to elude them.
Edna determines to hold on to her new-found independence, whatever the cost, and as she goes into the sea, that has always been a symbol of awakening and re-birth for her throughout the novel, she does not look back but goes on, experiencing memories of her childhood and recent past, wrapped in the sea's "soft, close embrace."
Therefore, to me, Edna's suicide was an act of sacrifice for herself. It was either this or to return to the socially prescribed roles of mother and wife that she rejected so strongly. Her suicide was an act of bravery and independence entirely in keeping with her own series of "awakenings" experienced through the novel. She is finally free to be the person she wants to be.