Even though she is jumpy as Macbeth is committing the murder, Lady Macbeth is definitely the stronger of the two in this act. She has asked the spirits to "unsex me here," and apparently they have. Lady Macbeth chastises Macbeth for not leaving the daggers at the scene in order to frame the guards and boldly takes them back to the grisly scene herself. She barks at him "what's done is done!" when he worries about not being able to pray or sleep from this point forward. She shows no guilt as she washes the blood from her hands and hurries the pair off to bed.
She continues her portrayal of the innocent woman when the body is discovered. She reacts as a shocked and grieving woman would, even fainting at one point. However, her plotting is seen through this fainting spell as she is trying to cover her husband's verbal slips.