The first exchange of speech between Juliet and her mother is when Lady Capulet asks if Juliet is awake, and Juliet says
Who is ’t that calls? Is it my lady mother?
Is she not down so late or up so early?
What unaccustomed cause procures her hither?
She doesn't immediately recognize her mother's voice, and the last line means, essentially, "what unusual reason does my mother have for coming here?" -- suggesting that her mother rarely comes to her room in the morning.
Later, when she thinks Juliet is mourning Tybalt's death, she is not very sympathetic:
Some grief shows much of love,
But much of grief shows still some want of wit.
In other words -grieving a little bit shows a lot of love. Too much grief shows you are stupid.
Lady Capulet shows that she completely misunderstands Juliet's grief when she says Juliet must be crying so much because Tybalt's murderer (Romeo) is still alive:
Well, girl, thou weep’st not so much for his death,
As that the villain lives which slaughtered him.
Lady Capulet continues to misunderstand, and doesn't see through Juliet's puns and double entendres about her anger and feelings for Romeo. Juliet says:
Oh, how my heart abhors
To hear him named, and cannot come to him.
To wreak the love I bore my cousin
Upon his body that slaughtered him!
Which means 'I hate hearing Romeo's name and not being able to chase after him. I wish I could take out my love for Tybalt on Romeo's body.' Sexy stuff! Her mother completely misses it.
Overall, Juliet and Lady Capulet are having parallel conversations. Like parallel lines, their words continue beside each other, but never really touch, because they are talking about two different things. This scene shows how Lady Capulet does not understand her daughter at all.