Who is Alcestis from The Year of Magical Thinking and what is their importance?

Alcestis is a character found in Greek mythology. She was a woman who agreed to give up her own life, so that her selfish stepson might be allowed to live. Because of her unselfishness, Alcesits is permitted by the gods to return to life. The woman who comes back from the dead, however, is a far different woman than the one who willingly went to her death.