Be careful with this quote, Lady Capulet does not know that Juliet is actually married to Romeo. However, this comment certainly functions to foreshadow the future as both fools who fall for Juliet end up married to "her grave". Lady Capulet is essentially washing her hands of Juliet here which demonstrates a great division in their relationship. Lady Capulet could actually care less about her daughter. She is almost wishing her daughter dead with this reference to the grave. She might be suggesting that there is no sense, no life left in this young woman. A girl always hopes that when division comes between herself and her father, a mother might be the one who tempers the relationship. That is not the case here, Lady Capulet takes the dad's side.