In act two, scene two, Lady Macbeth displays composure and maintains control over the tense situation by attempting to rationalize her husband's fears, calm him down, and finish executing the crime. When Macbeth initially leaves Duncan's chamber, he is visibly shaken and reveals his guilty conscience by saying, "This is a sorry sight" (2.2.20). Lady Macbeth corrects her husband by remarking that his comments stem from "foolish" thoughts.

Macbeth proceeds to say he heard one of the chamberlains remark "God bless us!" but laments that he could not reply by saying "Amen." Lady Macbeth continues to maintain composure and attempts to calm her husband's emotions by saying, "Consider it not so deeply" (2.2.30).

Macbeth then asks why he could not say "Amen," and Lady Macbeth tries to rationalize her husband's experience by encouraging him to forget about the crime and dismiss his active imagination. Despite Lady Macbeth's self-control and rational approach, Macbeth continues to grieve and elaborates on his auditory hallucinations. At this point in the scene, Lady Macbeth is fed up with her husband's behavior and tells him,

Why, worthy thane,
You do unbend your noble strength to think
So brainsickly of things. Go get some water,
And wash this filthy witness from your hand. (2.2.44-47)

By instructing her husband to wash the blood from his hands, Lady Macbeth is offering him rational, pragmatic advice to conceal his role in the crime. When Macbeth refuses to return the daggers to Duncan's chamber, Lady Macbeth takes matters into her own hands by placing the weapons next to the chamberlains.

Her ability to execute the plan to perfection and willingness to conceal their crime highlights her composure and control under extreme pressure. Unlike her husband, Lady Macbeth remains focused on concealing their involvement by manipulating the murder scene. Macbeth and his wife then hear Macduff knocking at the door, and Lady Macbeth offers her husband instructions by saying,

Retire we to our chamber.
A little water clears us of this deed.
How easy is it, then! Your constancy
Hath left you unattended...
Get on your nightgown, lest occasion call us
And show us to be watchers. Be not lost
So poorly in your thoughts. (2.2.67-71)

Lady Macbeth's comments regarding their crime and pragmatic instructions once again demonstrate her calmness under pressure and resolute nature. She understands the importance of making it seem as if they were sleeping during the crime and reiterates the importance of not allowing their thoughts to take possession of them.

Overall, Lady Macbeth demonstrates composure, self-control, and patience by encouraging Macbeth to calm down, following through with the crime, and taking careful precautions in order to get away with the assassination.

That which hath made them drunk hath made me bold.

What hath quenched them [Duncan's servants] hath given me fire.

Lady Macbeth maintains control of the situation (and her husband) in many ways in Act 2, Scene 2.  

First, she instructs Macbeth on how to think about the act he has just committed; when he claims, "This is a sorry sight," she replies, "A foolish thought, to say a sorry sight" (2.2.28, 2.2.29).  Further, when he expresses his anxiety about his inability to speak the word "Amen" immediately after he'd stabbed Duncan, she tells him to

Consider it not so deeply [....].  
These deeds must not be thought 
After these ways; so, it will make us mad. (2.2. 41-46)  

She wants him to stop obsessing about the murder because she fears that such obsessive thinking will ultimately drive them insane. They need to move on.

Second, Lady Macbeth alone has the foresight and wherewithal to properly frame the chamberlains for Duncan's murder. When Macbeth returns to her, he seems to be in shock and still carries the daggers he used with him.  She asks, 

Why did you bring these daggers from the place?
They must lie there.  Go, carry them and smear
The sleepy grooms with blood.  (2.2.62-64)

She knows that the murder weapons must be found with the servants if others are to believe they committed the murder.  When Macbeth refuses to go back into the room with Duncan's body, Lady Macbeth places the daggers there herself. When she returns to Macbeth, she chastises him for his cowardice, further showing the control she exercises over her husband:

My hands are of your color, but I shame
To wear a heart so white [....].
How easy it is, then!  Your constancy
Hath left you unattended.  (2.2.82-88)

While Macbeth laments the act, fears the eternal consequences of what he's done, and seems to cower before a corpse that cannot hurt him, Lady Macbeth manages the situation and her husband with apparent ease.  (Though we find out, later, that her conscience begins to eat away at her, too.)