What are some quotes that prove Lady Macbeth was only evil because it was necessary for her husbands sake?
In addition to the previous answer, there is another quote that highlights the nature of Lady Macbeth fulfilling Macbeth's prophecy.
I have given suck, and know(60)
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.
This statement goes against any ounce of feminine nature that can be traced in Lady Macbeth. She is explaining that she once fed a baby milk from her own breast, understanding the nature of that love and motherhood, but had she promised to dash the brains out of that babe for Macbeth, she would have done so. This statement is grotesque and shines an awful light on Lady Macbeth; however, it is important to understand that she would only do this out of a promise to Macbeth.
Lady Macbeth is often said to be evil from the get go, this however is not the case, our first meeting with Lady Macbeth see's her reading the letter sent to her by Macbeth explaining the witches prophecy.
Lady Macbeth has read the letter and started to think, at first she is estatic with the news.
"Glamis thou art, and Cawdor, and shalt be what thou art promised."
It is then suddenly she realises that for Macbeth to be King, he would have to do away with Duncan, but he lacks several qualitie that would make this possible.
" Yet do i fear thy nature. It is to full o' th' milk of human kidness to catch the nearest way. thou wouldst be great, are not without ambtion, but without the illness to attend it"
She realises that although Macbeth wants to be King he lacks the scruples to actually become King, it is with this in mind that she decides to help him, and to do this she has "cross over to the dark side"
" Hie thee hither that i may pour my spirits in thine ear and chastise with the valor of my tongue all that impedes thee from the golden round which fate and metaphysical aid doth seem to have the crowned withall."
the quote above can be seen as the first glimmer of"evil" from Lady Macbeth and relates directly to her helping Macbeth.
With this in mind, her solilquy in the next few lines can also be seen as her embracing evil to help her husband achieve the throne. Also when she adresses Macbeth upon his arrival home she tells him
" He thats coming must be provided for; and you shall put this nights great business under my dispatch, which shall to all our nights and days to come give solely soverign sway and masterdom."
This again highlights her plans to help her husband become King, whilst at the same time being"evil".
Other examples can include her telling Macbeth off in Act one Scene 7, when he tries to "chicken out" of killing the King, Lady Macbeth has already scarificed so much to get this fair (namely her giving up being a "woman") that she wades further into the darknes to help her hsband achieve King. I would recomend quoting from line 35-45, 48-59 and finally towards the conclusion of the scene where she outlines the plan to kill Duncan.
hope this helps