As the scene begins, Lady Macbeth is depressed. She has prodded her husband to perform a terrible murder that she had planned, and she feels that she has gained nothing from it:
Nought's had, all's spent,
Where our desire is got without content.
’Tis safer to be that which we destroy
Than by destruction dwell in doubtful joy.
Then Macbeth comes in and she tries to make him feel better:
How now, my lord! Why do you keep alone,
Of sorriest fancies your companions making,
Using those thoughts which should indeed have died
With them they think on? Things without all remedy
Should be without regard. What's done is done.
Of course, she contradicts herself here; she hasn't taken her own advice to heart. Macbeth then goes on about how disturbed he is, and Lady Macbeth tries again to calm him down:
Gentle my lord, sleek o'er your rugged looks;
Be bright and jovial among your guests tonight.
The scene ends as Macbeth suggests to his wife that more killing may make them both feel more at ease, but he leaves his plans a secret. She's curious, but surely no less depressed and disturbed. All in all, she contradicts herself only in an attempt to make Macbeth not feel what she so keenly feels.