There is no doubt that Lady Macbeth is power hungry. The mere hint of possibly being queen is enough to spur her toward the nefarious plot of killing King Duncan. I don't think that is the kind of power that you are asking about in your question though. I think that you are referring to power that Lady Macbeth exerts over people. I would say the best examples of that kind of power all occur within Act 1.
. . . and you shall put
This night's great business into my dispatch;
Which shall to all our nights and days to come
Give solely sovereign sway and masterdom.
The above quote occurs soon after Macbeth arrives home in Act 1, Scene 5. Lady Macbeth flat out tells her husband "leave everything to me." You might say that is not an example of power, but when Macbeth responds with more or less "okay," the reader gets the feeling that Macbeth is powerless when compared to his wife.
Later in Act 1, Scene 7, Lady Macbeth once again reasserts her power over Macbeth. Macbeth has decided to not go through with the murder, and Lady Macbeth is not happy about it. She berates and insults Macbeth until he agrees to kill Duncan. My favorite line in that sequence is this:
I have given suck, and know
How tender 'tis to love the babe that milks me:
I would, while it was smiling in my face,
Have pluck'd my nipple from his boneless gums,
And dash'd the brains out, had I so sworn as you
Have done to this.
Lady Macbeth tells her husband that she would smash a baby if she had agreed to do the deed in order to attain the throne. It's a disgustingly graphic guilt trip toward Macbeth, but it works. Macbeth turns around and murders Duncan.