In Act III, Scene 5, Juliet is no longer a helpless girl. She is a woman. She has married Romeo, and shared a wedding bed with him. Symbolically, she no longer belongs to her father. He cannot make choices for her. He may not know she married Romeo, but she knows that she is beginning another life. All she has to do is follow the plan, and the violence will be over. There will be nothing but romance.
Juliet still worries about Fate. She has a premonition that they will not be together again, and Romeo will die. She refuses to accept this fate.
O Fortune, Fortune! all men call thee fickle.
If thou art fickle, what dost thou with him(60)
That is renown'd for faith? Be fickle, Fortune,
For then I hope thou wilt not keep him long
But send him back. (enotes PDF p. 80)
When her nurse enters, the relationship between the two of them has changed, though Nurse does not realize it. Juliet is no longer a child needing comfort. She is playing a role, following through with the plan, scheming and tricking Nurse. She tells Nurse she does not feel well, and mourns Tybalt. She even says that she wants vengeance and Romeo dead!
Nurse responds by telling Juliet that everything is fine, because she is going to marry Paris. This is another turning point for Juliet. She can’t marry Paris, but she has to play along, playing the role of the good daughter until she can take the poison.
Juliet takes control of her fate in this scene. For the first time, she makes her own choice and is not a pawn in someone else’s game. She is still young, and she is afraid, but she finds her strength and takes the potion.
In Act 3, Scene 5, Juliet comes to the realization that she cannot trust her nurse and has been abandoned and isolated by her parents.