In the play "Romeo and Juliet by William Shakespeare, the author uses the nurse in many different ways. One of her useful functions is to give us access to Juliet's innermost secret feelings - clearly we see that she does not see her mom as a confidante, or even as a friend like the modern young girls of today. No, she sees her mom as someone to be obeyed, to respect but not to share her dreams with. The nurse,on the other hand, is very close to Juliet and they have a very warm affectionate bond. So, when Juliet confides things to her - we get to hear it, as the audience. The advice 'happy nights after happy days' could just as well apply to Romeo as to any other man Juliet might consider, so perhaps she has this on her mind.
I am not sure where in the play you are thinking of, or where your teacher means you to find this answer.
However, I think that the best answer to this comes from Act I, Scene 3. In this scene, Lady Capulet has been talking to Juliet about marrying Paris. Juliet is not sure, but is willing to do whatever her mom says, more or less.
At the end of the scene, Lady Capulet has left, and the Nurse ends the scene by telling Juliet that she should find a man who will give her happy nights after happy days.