In Macbeth Act 1, Scene 5 (only), what does the audience learn about Lady Macbeth that it didn't know before?
It is this particular scene which proves that Lady Macbeth is rightly termed as the 'fourth witch' of the play. In order to emphasize this,Shakespeare has introduced this character to the audience by having her on the stage alone!She is prepared to be tempted by the devil and at a point she even invokes the devil by calling upon the spirits to take away her femininity, to thicken her blood and take away from her the ability to weep:
"Under my battlements, come you spirits,That tend on mortal thoughts,Unsex me here,And fill me from the crown to the toe, top-full Of direst cruelty: make thick my blood,Stop up th’ access and passage to remorse,That no compunctious visitings of natureShake my fell purpose”
Therefore you can say,Lady Macbeth has been endowed with all the blessings of Shakespeare's most strongest female character. Hence,all that one can deduce regarding Lady Macbeth's characteristic traits from this scene is that of:strong will power,ambitious,ruthless,murderous,devilish,atheist,power-hungry,low regard for her husband,self-centered/selfish and above all non-motherly. Maybe this was a reason why Shakespeare decides to give off springs to Banquo,Macduff and his Lady Macduff whereas he deprives Macbeth and Lady Macbeth for the same.