Lady Macbeth is shown to be vile the first time we meet her in Act 1 Scene 5. She reads the letter Macbeth has sent ahead to her to share his good fortune (and tell her what the witches predicted), and she responds as follows:
Glamis thou art, and Cawdor; and shalt be
What thou art promised: yet do I fear thy nature;
It is too full o' the milk of human kindness
To catch the nearest way: thou wouldst be great;
Art not without ambition, but without
The illness should attend it: what thou wouldst highly,
That wouldst thou holily; wouldst not play false,
And yet wouldst wrongly win: thou'ldst have, great Glamis,
That which cries 'Thus thou must do, if thou have it;
And that which rather thou dost fear to do
Than wishest should be undone.' Hie thee hither,
That I may pour my spirits in thine ear;
And chastise with the valour of my tongue
All that impedes thee from the golden round,
Which fate and metaphysical aid doth seem
To have thee crown'd withal.
In other words, you're already Thane of Glamis and Cawdor and will be what fate decrees you'll be (king), but I'm afraid that you're too good of a man to make it happen as soon as possible. You are ambitious but you're too honorable to do what must be done if I'm to be queen immediately. Therefore, I'll say whatever I must to make you do what must be done.
(It's important to remember that if Macbeth is fated to be king, he will be even if he doesn't become a villain. That's what "fate" means.)
When she hears that King Duncan and his entourage will be their guests, she asks evil spirits to make her more manly so she can commit murder. This is utterly vile because Duncan is a good king (in Shakespeare's play, anyway), and because hosts had a sacred duty to protect any guests in their home, even when those guests weren't royalty.
When she welcomes Duncan in Scene 6, she tells him that she and Macbeth are his servants, and whatever is theirs is his. She's a blatant liar, smiling to his face when she has already decided he will never live to see the morning.
In Scene 7, Macbeth thinks about the plan and decides to not do it for many honorable reasons, not the least of which is his fear of hell. When Lady Macbeth hears this, she insults his manhood and says that if she'd promised as he had to kill Duncan (which he hasn't), she'd take a helpless infant from her breast and bash its brains out before she'd go back on her word.
Perhaps you can see that she is vile in every conceivable way.