This quote is taken from Act III, Scene V, and is spoken by Juliet's mother, Lady Capulet. To put this into context, Juliet has refused to marry Paris, and her parents are both annoyed and exasperated by her feelings on this subject.
In terms of its literal meaning, Lady Capulet is saying here that her daughter is a "fool" for not wanting to marry Paris. Moreover, Lady Capulet wishes that Juliet were dead and, therefore, married to her grave. Looking deeper, Lady Capulet's fury is apparent: she cannot understand why Juliet would refuse such a handsome and successful suitor. She is so angry that she would rather see Juliet dead than have her daughter continue on this path of complete defiance. After all, in this setting it is a woman's duty to get married and to have a family. By marrying well (with Paris), Juliet ensures the prosperity and respectability of the Capulet name and the Capulet family.
Of course, Lord and Lady Capulet have no idea that Juliet is refusing Paris because she has already married Romeo and, earlier in this scene, has consummated that marriage.