It begins with the letter Macbeth sends her. She reads it aloud and tells us that her husband is too nice (too full of the milk of human kindness to catch the nearest way) to do what is necessary to make their dreams come true.
She continues by telling Macbeth to "look like the innocent flower but be the serpent under't"--put on a friendly face but think black thoughts and murder toward Duncan.
Later on, when she begins sleepwalking, she talks of how she still sees the spot of blood on her hands and that all the perfumes of Arabia can not sweeten her horrible hands. Her guilt and conscious are overwhelming her until she finally commits suicide.
She is never what I would call on a normal plane. She begins as an evil woman who cares about no one but herself and her own family (aside from the fact that she said she would dash the brains of her own child onto the ground had she known her husband was such a coward). She is greedy and very manly, pushing her husband to do what she wants. After he abandons her and they are no longer such a tight-knit "team," she unravels and ends her life as violently as she lived it.
In Act V, scene i, Lady Macbeth's conscience is catching up with her. She reenacts washing Duncan's blood off her hands, yet continuously finds a spot... her insistant, "Out , damn spot!" shows that her hands will never be clean of Duncan's blood, nor will her soul. It is ironic that Lady Macbeth is the one who convinced her husband to kill the king, all while talking about how tough and strong she is (even to the point of saying she would dash out a newborn babe's brains!) if it would get her what she wanted. Her husband, the hesitant one at the time, is now the ruthless killer, actually having McDuff's entire family (children included) killed. The so called "stong" (Lady Macbeth) became weak as her conscience wore on her. She sleepwalks, "washes" her hands, and cries out in her madness. Her "weak" husband doesn't even bat an eye when he learns of her death!