Lady Macbeth’s speech?Watch
Why does Shakespeare have Lady Macbeth do this? And would it be possible that Lady Macbeth might have been played by an actor who was also playing one of the witches in Shakespeare’s original productions?
another interpretation of Lady Macbeth is that she could be a fourth witch - i personally didn't explore this concept too much but here's some webpages that mention the idea: here and here.
hope this somewhat helps!