This is an interesting question to consider, because Lady Macbeth, unlike her husband, does not seem to have any external influences. Macbeth is a character who is influenced so greatly by others: by the witches and by his own wife. Lady Macbeth, on the other hand, seems defined by her own internal influences rather than anything else. The only hint that we have of any external influence upon her is in Act I scene 5 when she reads Macbeth's account of meeting the witches and the prophecy they gave him. She clearly is impelled to act the way that she does thanks to the prophecy of the witches, but we are convinced that her resolute and ruthless character emerges not from any outside influence but from her own identity and character. Consider the following lines, for example:
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...
She displays a particularly astute understanding of Macbeth's character and her plan to persuade Macbeth to do what he has to do in order to become king is something that emerges from within her rather than being the result of any exterior influence.