Death
Death is a major theme of the play, as we hear B tell C that she must begin to think of death. A is on her deathbed in Act II, and in a poetically sad way, C learning of what is to come in her life represents the death of her youth, her dreams and her hope of the kind of life she believed was ahead for her.
Regret
This theme is seen represented in the son who comes back to his dying mother's bedside in Act II. He never speaks, which is deeply representative of not being able to say the things one desires to say before their parents pass on. We also hear from A that she never forgave him for leaving, whether she regrets that or not isn't clear, but plays into how one will never know as she is no longer living and able to do so.
Memory
Memory is a major theme of this play; we see A reminisce in memories of her life as a child and younger woman. We hear of what she's lost and the things she never had. A and B's memories become C's future for better or worse, which the young woman is set on not allowing to happen to her. The memories for the two older women become what C will fight against becoming.