What evidence is there in the beginning of the Macbeth play to indicate that Lady Macbeth is not inherently evil?
In my opinion there is not a lot of evidence to support this, but there is at least some evidence to support the idea that Lady Macbeth isn't a crazy, evil psycho right from the very beginning.
Lady Macbeth is introduced to the audience in Act 1, Scene 5. She is reading a letter from Macbeth in which he narrates his encounter with the witches. Her initial response is shock and surprise at his promotion and prophecy. She quickly grasps on to the idea that in order to be king, something bad would have to happen to Duncan. Lady Macbeth admits to the audience that her husband doesn't have it in him to do it.
. . . yet do I fear thy nature;
It is too full o' the milk of human kindness
To catch the nearest way:
She knows that Macbeth is too kind of a person to kill Duncan. That means Lady Macbeth knows that she must take it upon herself to "encourage" her husband to take the necessary steps to be king.
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.
Lady Macbeth is more or less saying that she's not evil. She just has to become evil for her husband's sake.