In Macbeth, Lady Macbeth is dedicated to Macbeth and is prepared to go to great lengths to ensure that he successfully ascends the throne of Scotland. As soon as she hears about the witches' prophesies, she makes plans, even calling on the spirits to "unsex me here," (Act I, scene v, line 38), meaning that she would like to be rid of all compassion which otherwise may prevent her from carrying out whatever deed may be necessary.
In Act II, scene ii, Lady Macbeth is feeling "bold" (1). She has ensured that Duncan's guards are deeply asleep because she made sure that she drugged their wine which will enable her to place the blame squarely on them when Duncan's murder is discovered later. When she hears Macbeth approaching, she is momentarily concerned, even though she even laid the daggers ready, making it easy for him and only wishes that Duncan had not resembled her father so much because then she would have murdered him herself, such is her resolve.
Macbeth is clearly confused after the murder and Lady Macbeth tries to comfort him and tells him not to worry. She suggests that he is thinking about the events too much and will feel better if he stops worrying and washes "this filthy witness from your hand" (47). When she sees that he is carrying the daggers with which he killed Duncan and will not return them to Duncan's chamber, she undertakes it herself at great risk. She is advising and calming Macbeth to ensure that he does not give himself away.
By Act III, scene iv, the banquet is prepared at Macbeth's castle and, unbeknownst to Lady Macbeth, Macbeth has arranged for Banquo's murder. He has just heard that, although Banquo is dead, his son Fleance is still alive, which threatens Macbeth's future. Macbeth comments, "I had else been perfect" (21). It is essential that the banquet goes well but, immediately, Lady Macbeth realizes that something is wrong with a delusional Macbeth and she suggests that he is suffering from a fit; something that he has lived with since childhood. When he continues, she placates the guests and eventually suggests that they leave to allow Macbeth to rest. Lady Macbeth tells Macbeth to sleep as she thinks he is sleep-deprived after Duncan's murder. She does not realize, at this stage, that Banquo is dead. Her resolve in protecting Macbeth is unquestionable.