Marsha Norman wrote 'night, Mother and this modern tragedy touches on many themes. Essentially Norman shows how wasted a life can be when there is no real communication between people.
Jessie, the daughter, has decided to take her own life. In the 90 minutes before she dies, she and her mother have what is probably the most insightful conversation of their lives. But even so, it is too late to repair a lifetime of dysfunction.
Mama has isolated Jessie because of Jessie's epilepsy. When Jessie is older and finally has her disease fairly well controlled, she is too frightened to try to establish any kind of normal life outside the walls of her home and caring for her mother. This feeds her depression.
Norman also shows how isolation occurs when one has too much of one's own identity wrapped up in other people. Jessie sees her brother and her son, both of whom she loves, as complete failures. When her husband left her, she wrote an entire letter detailing how he must have felt. She still loves him as well, but the marriage could not work.
Her main purpose in life is to care for her somewhat self-absorbed mother, and that is hardly fufilling. Jessie has no sense of personal identity or well-being. In the end this becomes a catalyst for her self-destruction.