Understanding why Lady Macbeth has begun to sleepwalk will help you to understand her character.
She needs to be cleansed. Lady Macbeth never saw the evil of the murder lasting in this way. The blood of Duncan haunts her.
She re-runs her own part in the murder to come to terms with her guilt. An important point. She does not try to blame anyone but herself. Her words come back to haunt her.
Lady Macbeth is horrified by Macbeth's continued killing. She was devastated by the slaughter of Lady Macduff and her children. What does the scene tell us about her part in the play?
As a woman, Lady Macbeth never had the power to control things independently. The sleepwalking scene is intimate. While Macbeth's conscience strikes in a public banquet, Lady Macbeth's fear shows up in a private setting. This underlines the different roles of men and women in this society.
Lady Macbeth always saw an end to the process and thought once Duncan was dead, power would rest with herself and Macbeth. This is probably the most important point. She goes over this point in her head.
She was never really an evil person. It was Macbeth who had faith in supernatural powers. Lady Macbeth invited them in, they possessed her, and have left her powerless.
The isolation has driven her mad as Macbeth no longer seems to exist for her, Lady Macbeth always instinctively saw herself as part of a couple. Macbeth has gradually broken away from her, leaving her totally isolated in her chamber. She desperately wants their former closeness.