What is the attitude of Lady Capulet toward Juliet's defiance?
I think the scene that you are referring to is Act 3, Scene 5. Lady Capulet enters and thinks that Juliet has been crying over Tybalt's death. Lady Capulet and Juliet do some verbal punning at this point. Lady Capulet says that Romeo needs to die, and Juliet intricately states her love for him while making her mother think that they agree with one another.
Lady Capulet then drops the news of Juliet's intended marriage to Paris on Thursday. Juliet responds by saying:
"He shall not make me there a joyful bride.
I wonder at this haste; that I must wed
Ere he, that should be husband, comes to woo.
I pray you, tell my lord and father, madam,
I will not marry yet; and, when I do, I swear,
It shall be Romeo, whom you know I hate,
Rather than Paris."
I absolutely love how Lady Capulet responds. She doesn't get angry the way that Capulet does. She stays calm, and tells Juliet to tell her father the same thing. It's the classic "we'll see what your father has to say about that" line.
"Here comes your father; tell him so yourself,
And see how he will take it at your hands."
Capulet, on the other hand, blows a gasket. He yells at Juliet, calls her names, and threatens to throw her out. To Lady Capulet's credit, she tries to keep her husband calm and tries to reign in some of his threats. Lady Capulet is unsuccessful in her attempts to calm down Capulet, but she never disagrees with him. At the close of the encounter, Juliet pleads with her mother to change her mind and speak with Capulet. Lady Capulet refuses to help and walks away. She basically tells Juliet that the conversation is over and doesn't want to hear another word.
"Talk not to me, for I'll not speak a word:
Do as thou wilt, for I have done with thee."