In Act I scene 7, Lady Macbeth swears she would've killed her own child, had he asked her to in the following (yet morbid) quote: "I would, while it was smiling in my face, have plucked my nipple from his boneless gums, and dashed the brains out, had I so sworn as you have done to this."
After Macbeth kills Duncan in Act II scene 2 and is fumbling around with the bloody daggers, Lady Macbeth takes control of the situation and says, "Give me the daggers." She places them by the guards. Then she says, "Get on your nightgown...be not lost so poorly in your thoughts." She makes him think clearly and return to "normal" so they can act surprised when the king is found dead.
One other instance is in Act III scene 4 when Macbeth sees Banquo's ghost. Lady Macbeth clears the room because she sees that he's going crazy and doesn't want the noble men to find out of their dirty deeds. She tells the noblemen, "At once, good night. Stand not upon the order of your going, but go at once."