Answer:
4.)To do so would reveal her own hesitation and failure to act after she has criticized Macbeth for his.
Step-by-step explanation:
Lady Macbeth doesn´t kill Duncan in his sleep because he resembles too much of her own father, but still she doesn´t want to tell this to Macbeth because she has critized Macbeth for this kind of hesitations before, so she decides to not tell anything, also it is important for the play that Macbeth is the one that actually kills Duncan because the whole play is about everything he is willing to do in order to become King.