In Macbeth, Lady Macbeth is the driving force behind her husband, Macbeth, as they plot his rise to the throne of Scotland. Macbeth has shown valor and has been awarded by the king for his achievements in battle - common in Shakespeare's day- and will become Thane of Cawdor.
Macbeth has also been "visited " by the weird sisters (the witches) who have prophesied that he will in fact be King of Scotland. Lady Macbeth is not content to wait and see if the prophesies come true and as soon as she learns of the prophesies she starts scheming as to how to make them real. She is prepared to go to great lengths and asks to be filled "from the crown to the toe, top-full of direst cruelty" (I.v). She is prepared to "unsex" herself if necessary and tells Macbeth to "leave all the rest to me."((I.v)
After Macbeth kills Duncan, Lady Macbeth is pleased and does not feel guilty as he does . She tells Macbeth "a little water clears us of this deed"(II.ii). However, as Macbeth becomes more murderous, she becomes increasingly plagued by doubts. Macbeth excludes her from his future scheming although she still tries to protect him. After he kills Banquo and is seemingly distracted by his ghost, she ensures that guests leave quickly after his "episode" and she is the one to reassure everyone.
In Act V.i. she has been driven mad by her involvement in these heinous (terrible) deeds and wonders about her responsibility for Macbeth's killing spree. The doctor has been called because Lady Macbeth is rambling and is intent as she tries to "wash" away her guilt:"Out damned spot!"(V.i). That no longer works for her.
The doctor cannot understand her madness and there is no physical cause. The doctor knows that "this disease is beyond my practice" and that Lady Macbeth needs "the divine " more "than the physician."
It must be said that, even at this late stage of her madness, she still tries to protect Macbeth, even in his absence as she calls him "to bed, to bed, to bed!"