How and why does Juliet's relationship with the Nurse change? Is Juliet justified in her feelings toward the nurse?

The Nurse is Juliet's closest companion and confidante in Shakespeare's Romeo Juliet. Juliet confides in the Nurse about her most intimate secrets, especially her love for Romeo. She is, in fact, closer to the Nurse than her own parents, as evidenced by the discussion with Lady Capulet in Act I, Scene 3, which is dominated by the Nurse. The Nurse is also a foil to Juliet. A foil is a character who provides a...

The Nurse is Juliet's closest companion and confidante in Shakespeare's Romeo Juliet. Juliet confides in the Nurse about her most intimate secrets, especially her love for Romeo. She is, in fact, closer to the Nurse than her own parents, as evidenced by the discussion with Lady Capulet in Act I, Scene 3, which is dominated by the Nurse. The Nurse is also a foil to Juliet. A foil is a character who provides a contrast to another character. For a more complete discussion of how the Nurse is a foil to Juliet see the link below.

In Act III, Scene 5, Lord Capulet breaks the news to Juliet that he has promised her in marriage to Count Paris. When Juliet refuses (she is already married to Romeo), Capulet flies into a rage and berates his daughter, threatening to disown her. At first the Nurse attempts to defend Juliet. She says,

God in heaven bless her!
You are to blame, my lord, to rate her so.

But later, after Capulet has left, the Nurse advises Juliet to forget Romeo (he has been banished to Mantua) and marry Paris. She does not understand the devotion Juliet feels for Romeo. She even tells Juliet that the Count is a better man. She says,

Faith, here it is.
Romeo is banished, and all the world to nothing
That he dares ne’er come back to challenge you,
Or, if he do, it needs must be by stealth.
Then, since the case so stands as now it doth,
I think it best you married with the County.
O, he’s a lovely gentleman!
Romeo’s a dishclout to him. An eagle, madam,
Hath not so green, so quick, so fair an eye
As Paris hath. Beshrew my very heart,
I think you are happy in this second match,
For it excels your first, or, if it did not,
Your first is dead, or ’twere as good he were
As living here and you no use of him.

This, of course, is not what Juliet wants to hear. She feels betrayed by the one person she thought would understand. At the end of the scene, she thanks the Nurse and dismisses her. It is the last conversation they ever have. She then reveals her negative response to the Nurse's advice. She doesn't understand how the Nurse could originally praise Romeo and then denounce him. She vows to never listen to the Nurse again:

Ancient damnation, O most wicked fiend!
Is it more sin to wish me thus forsworn
Or to dispraise my lord with that same tongue
Which she hath praised him with above compare
So many thousand times? Go, counselor.
Thou and my bosom henceforth shall be twain.

Juliet is definitely justified in her response to the Nurse. She could not marry Paris and it was hypocritical for the Nurse to change her mind about Romeo. Juliet needed more constructive advice from the Nurse. Instead she turns to the Friar, whose plan is ultimately fatal.