Juliet's mother comes to Juliet in Act III, Scene 5 to tell her that she is to marry Paris on Thursday, Lady Capulet believes that these are "joyful tidings". When Juliet responds that she will not marry now, Juliet's mother has Juliet tell her father her response so Juliet can bear the brunt of her father's anger.
Lady Capulet: "Here comes your father: tell him so yourself,/ And see how he will take it at your hands".
When Lord Capulet hears Juliet's response he is enraged and tells Juliet that she will marry Paris or he will cast her out of their home and she will be left to die in the streets.
Lord Capulet: "Graze where you will, you shall not house with me:/ Look to't, think on't, I do not use to jest./ Thursday is near; lay hand on heart, advise:/ An you be mine, I'll give you to my friend;/ An you be not, hang, beg, starve, die i' the streets,/ For, by my soul, I'll ne'er acknowledge thee,/ Nor what is mine shall never do thee good".
When Juliet asks her mother for help against her father's anger her mother responds, "Talk not to me, for I'll not speak a word;/ Do as thou wilt, for I have done with thee", and refuses to help her.
Her mother's behavior is consistent with Elizabethan times, where a father's will is paramount - but as modern readers it influences our opinion of her in that she shows little concern for her daughter and her wishes. We see her as cold and uncaring for Juliet and a contributor to her ultimate death.