For one thing, she puts her husband, Macbeth, to murder the king in order for him to take the throne. Macbeth by nature is not a cruel person by heart but he does not possess the power, ego and wickedness that Lady Macbeth possesses. Add to the act that they are in love with each other and you can see how Lady Macbeth can see anyone as a potential tool, even her own husband.
She makes her intentions clear from the beginning:
"...Come you spirits,
That tend on mortal thoughts, unsex me here,
Of direst cruelty. Make thick my blood;
Stop up th' access and passage to remorse,
That no compunctious visitings of nature
Shake my fell purpose nor keep peace between
Th' effect and it. Come to my woman's breasts
And take my milk for gall, you murd'ring ministers
Whereever in your sightless substances
And pall thee in the dunnest smoke of hell,
That my keen knife see not the wound it makes,
Nor heaven peep through the blanket of the dark
To cry 'Hold, hold.'"
Part of her speech reflects that Lady Macbeth is fully aware of a woman admists a patriarchial warrior society. Part of the reason she does not seek to kill Duncan herself is society's fault, for Lady Macbeth was simply not trained to effectively kill another person. She uses her sharp wit and potential of love to goad Macbeth to committing the deed that would doom him to the end of the play. Lady Macbeth also uses the blood stained daggers that were in Macbeth's possession to frame the guards responsible for protecting King Duncan's life.
Does that mean she is a one-dimensional monster? Lady Macbeth gives off a very good appearance of being a cold, calculating creature with her ability to use a power to goad others into what she desires. She craves power far more than what Macbeth originally wanted and she infects hm with that hunger to rule and to kill without opposition. But like her husband Macbeth, she possesses a mortal conscience. With the deaths mounting, the new "Queen" of Scotland goes mad:
"Out, damned spot! Out, I say! One-two - why then 'tis time to do't. Hell is murky. Fie, my lord, fie! A soldier and afeard? What need we fear who knows it, when none can call our power to account? Yet who would have thought the old man to have had so much blood in him?"
It can be assumed that Lady Macbeth's madness is attributed to guilt, that she helped the deaths of important people within the play. Macbeth was a reluctant murderer but Lady Macbeth thought that she was a born murderess but was proven gravely mistaken. If we are to see her cries as guilt, we can see that Lady Macbeth is a potential murderer but not a sociopath.
Lady Macbeth like other Shakespeare's characters have made their mark on popular culture. The recent addition of her liking is the historical novel Lady Macbeth by Susan Fraser King. It is a new take on the classic villainess set in the role as the protagonist.
Yes, Lady Macbeth is someone you would not want to confront at a conference table but she turned out to be one of my favorite characters in Shakespeare's world. Why she is a favorite is possibly for the wrong reasons. She is powerful, able to seduce at a subtle level and is memorable. There are many people in real life, male and female, who have a mixture of power, seduction and vicious wit. Those all make a dangerous combination.