What evidence from the text supports Lady Macbeth being called "the fiend-like queen" in Macbeth?

Lady Macbeth is fiend-like because she is ruthless and ambitious. 

A fiend is a derogatory description. It is best defined as “villain” or “devil.” Lady Macbeth has this reputation because she wanted her husband Macbeth to be king so badly that she talked him into killing the king and would not take no for an answer. 

Lady Macbeth is not very feminine. She is just as ruthless and ambitious as her husband. You could say she is actually more ambitious, because when her husband tells her about the witches’ prophecies, she says in a soliloquy that she fears he does not have it in him to make them come true:  

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 (Act I, Scene 5).

Additionally, Lady Macbeth gives a positively chilling speech about her womanhood. She asks to be unsexed, or made into a man, at one point. She also claims that she would be willing to bash a baby’s brains out to get what she wants. 

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 (Act I, Scene 7). 

When Macbeth dithers about whether or not he should kill Duncan, Lady Macbeth nags him. He worries Duncan did nothing to deserve to die, and that as his host he should be protecting him and not killing him. He is also concerned they might get caught. When he asks Lady Macbeth what will happen if they fail, she says that if he is brave enough they won’t possibly fail. By saying this, she puts it all on him. 

Lady Macbeth plans the murder out carefully. She even scolds Macbeth for not following the plan to the letter when he brought the daggers with him that he used to commit the killings. She reminds him that he was supposed to leave them by the bodies as part of the frame-up. 

When Macbeth acts so strangely during the banquet after killing Banquo, Lady Macbeth makes excuses for him. She tells everyone he is “often thus” and it is no big deal. She then chides Macbeth in private, asking him, “Are you a man?” Of course, we know Lady Macbeth is not immune to guilt. She has a little nervous breakdown of her own, where she can’t wash the metaphorical blood off her hands.