What quotes provide evidence that Lady Macbeth knows right from wrong in Shakespeare's Macbeth?
In another of Shakespeare's plays, a conflicted Hamlet reflects in one of his soliloquies, "Thus doth conscience make cowards of us all." Lady Macbeth also struggles with her conscience, which controls some of her actions and later even causes her demise.
While she has called upon the spirits to "unsex" her in Act I, Scene 5, so that she can become bolder, Lady Macbeth is not rid of her conscience after her invocation of these evil spirits. For although she feels "bold," afterwards, she remarks that she would have killed King Duncan herself "[H]ad he not resembled/ My father as he slept" (Act II, Scene 2, lines 12-13). Indeed, her conscience has made her a "coward," too.
Later in this scene, Lady Macbeth scolds her husband for having "a heart so white" that he is disturbed after his act of regicide since Macbeth declares that "all great Neptune's ocean" cannot wash the blood from his hands. She reduces his figurative language to the mundane as she tells Macbeth, "A little water clears us of this deed" (Act II, Scene 2, line 65). Later in the play, however, Lady Macbeth's conscience bothers her so much that she obsessively tries to wash blood spots off her hands in a delusional state:
Out, damned spot; out, I say. One, two,—why, then ’tis time to do’t. Hell is murky (Act V, Scene 1, line 30).
In this final act, Lady Macbeth is completely destroyed by her guilt and has descended into madness. Tragically, it is her conscience that causes the death of Lady Macbeth.
The quote in Act 2, Scene 2, lines 12-13, "Had he not resembled/my father as he slept, I had done't" indicates that Lady MacBeth does have some conscience.
The quote indicates that she has some knowledge of right and wrong because she shows compassion towards King Duncan by relating the appearance of the sleeping Duncan to memories of her father. The fact that she states she could not kill him as he slept there, helpless, resembling her father, indicates to the reader that she is not purely evil.
If you are searching for other instances of Lady MacBeth's humanity, consider this- it can be interpreted that guilt drove her mad. The idea that one could be so consmed with guilt that she hallucinates and eventually ends her life certainly shows knowledge that her actions were wrong. While I find this a compelling argument for her humanity, some may argue that Lady MacBeth's eventual insanity was a result of stress, pressure, or fascination, not guilt.
For more information about Lady MacBeth's character, I've linked to her character analysis.