The nurse's behavior changes based on a change in the tension of the story.
We can arrive at this answer because:
The nurse was someone who raised Juliet since she was a baby.
The nurse cares about Juliet a lot and wants her to be safe and happy.
In this case, the nurse's behavior is always positive to the things Juliet wants.
However, when there is a change of tension in the story and Juliet's happiness is put at risk, the nurse changes her behavior and is opposed to these situations.
An example of this can be seen when the nurse encourages Juliet to marry Parris and abandon the feelings she has about Romeo. She behaves this way because she thinks Romeo will make Juliet unhappy and put her in danger.
As you have not informed the act to which this question refers, I can't provide a specific answer, but I hope that the information above can help you.
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