What does the soliloquy by Lady Macbeth in Act I, scene v of Macbeth suggest about her psychological state?

In Act I of Macbeth, Lady Macbeth's character is much more stable and composed than she is later in the play (namely, Act V). In Act I, scene v, Lady Macbeth receives a letter from her husband, who is on his way home from battle. In the letter, Macbeth tells his wife that after leaving the battlefield, he and his friend Banquo were met by three witches who predicted that Macbeth will be king....

In Act I of Macbeth, Lady Macbeth's character is much more stable and composed than she is later in the play (namely, Act V). In Act I, scene v, Lady Macbeth receives a letter from her husband, who is on his way home from battle. In the letter, Macbeth tells his wife that after leaving the battlefield, he and his friend Banquo were met by three witches who predicted that Macbeth will be king. We can analyze Lady Macbeth's mental state by examining her reaction to this news in Act I, scene v.

Lady Macbeth's first reaction to the letter is to assert that Macbeth deserves to be king and will get what he deserves. She is strong-willed, determined, and confident here. She does note that Macbeth can be "too full o' the milk of human kindness," meaning that he may not be able to commit such an evil act as murdering King Duncan in order to take his position (line 18). As a result, Lady Macbeth knows that she will have to be strong and assertive. In her famous soliloquy, she wishes to remove her feminine qualities (those associated with weakness) that would lead one to assume a woman like herself could not commit a cruel and ambitious act. Lady Macbeth asks "spirits" to "fill [her] from the crown to the toe top-full/ Of direst cruelty" (41, 43-44). This may imply that Lady Macbeth is not by nature evil but that she also has more faith in her capacity for cruelty than she has in her husband. In this scene, Lady Macbeth is focused on the goal: to ensure her husband takes the throne of Scotland. 

Lady Macbeth's mental state in this scene is composed, confident, and relatively stable. Although she is asking for help to be cruel, which may seem paradoxical, her clear thinking in this scene is a stark contrast to the Lady Macbeth we see in Act V, when she is trying desperately to remove an imaginary stain of blood from her hands.