I agree entirely but would like to add that our introduction to Lady Macbeth is when she reads the letter from Macbeth telling her what has happened. She is then informed by a messenger that Duncan will be visiting. She sees her chance to help the third prophesy come true but knows she cannot do what must be done since she is a woman and has a woman's nature. She calls upon the dark powers to unsex her. Whether or not her prayers are really answered, we don't know. What we do know is that she believes that they have been.
In order for her to get the blood on her hands, Macbeth must bring the daggers with him after he kills Duncan and refuse to return to the scene of the crime. In her innocence she tells him that a little water washes the blood away as if their guilt will disappear with it.
Whether the spirits she prayed to answered her but have withdrawn their"protection" or the reality of the murders begins to weigh up her conscious is a choice for the actress playing the role.
By the time we get to the sleepwalking scene, she is already in hell and is reliving all the murders from Duncan to Macduff's wife. Her only way out is death.
Lady Macbeth is onstage quite a bit in the early Acts of the play, but after the end of Act III, scene iv -- the Banquet scene -- she all but disappears from the play, returning for her last appearance onstage in one of the most famous scenes in Shakespeare's canon -- the Sleepwalking scene -- Act V, scene i. So, there isn't much progression towards madness to show, as it happens offstage, while the title character of the play, Macbeth, devolves further and further into his murders and schemes onstage.
She seems to have all in hand in Act III, scene iv, even though Macbeth has done a pretty effective job of blowing their cover by freaking out over the appearance of the ghost of Banquo, a ghost that no one sees but him. She has tried her best to do damage control during the banquet, but the other Thanes have left the feast with their suspicions roused against Macbeth. The only hint of the progression towards madness that Lady Macbeth will undergo is the exchange between Macbeth and Lady Macbeth at the very end of the scene:
You lack the season of all natures, sleep.
Come, we'll to sleep. My strange and self-abuse
Is the initiate fear that wants hard use.
We are yet but young in deed.
And though this looks like simply words of comfort from Lady Macbeth, it foreshadows her inability to sleep later in the play and the madness that accompanies it. So this conversation hints that the progression towards that obviously manifests for her offstage between this time and Act V.
In the early scenes of the play, it is Lady Macbeth who is completely resolute, even scoffing at what she considers Macbeth's cowardly behaviour just after he has murdered Duncan:
My hands are of your colour; but I shame
To wear a heart so white. (II,ii)
And, while Macbeth grows in thick-skinned-ness throughout the play and the murders he commits, Lady Macbeth declines into a guilt-ridden madness that will not let her sleep. In Act V, scene i, she says:
The thane of Fife had a wife. Where is she now?...Here's the smell of blood still. All the perfumes of Arabia will not sweeten this little hand.
The reference to her hands reeking of blood is a nice reference back to the early scene in which she gloried in her bloodied hands and chided Macbeth's fear. And to say that Macbeth "had a wife," but wonder "where is she now," indicates that she has changed so much as to have become a different person.
So, though the progression that Lady Macbeth undergoes happens offstage, Shakespeare makes some nice connections between early and later scenes to give the audience a sense of what has driven her to madness and death. Please follow the links below for more details about the character of Lady Macbeth.