At the beginning of the play, Lady Macbeth has more power, but as Macbeth gets more ambitious he overtakes her.
As the play begins, Macbeth listens to the witches’ prophecies and passes them on to his wife. She is thrilled that the witches were correct in seeing his promotion, and excited by the prospect of him becoming king. When he is not named successor, she is ready to encourage him.
Lady Macbeth knows that her husband is not going to act on his own.
Yet do I fear thy nature;
It is too full o’ the milk of human kindness(15)
To catch the nearest way. Thou wouldst be great;
Art not without ambition, but without
The illness should attend it. (Act 1, Scene 7)
She decides to push him, and does so with a combination of sweet-talk and insults. She encourages him to kill Duncan, even when he does not want to. She gets her way, not only telling him what to but exactly how to do it.
After Macbeth kills Duncan, the balance of power changes. Macbeth begins to keep things from his wife, and tells her to not worry and leave things to him.
Be innocent of the knowledge, dearest chuck,(50)
Till thou applaud the deed. (Act 3, Scene 2)
As Macbeth kills more and more people, he pushes her away. Eventually she breaks, losing her mind and committing suicide.
She acknowledges her part in creating the monster he has become, and succumbs to the guilt. Macbeth, on the other hand, barely acknowledges her death as he continues in reckless ambition.