"Indeed, I never shall be satisfied
With Romeo till I behold him—dead—
Is my poor heart, so for a kinsman vexed.
Madam, if you could find out but a man
To bear a poison, I would temper it,
That Romeo should, upon receipt thereof,
Soon sleep in quiet. O, 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 hath slaughtered him."
I think you are referring to this sequence. Lady Capulet has come to Juliet's room for two reasons. First, to console Juliet over Tybalt's death. Second to inform Juliet about her marriage to Paris. Lady Capulet talks of having someone find and kill Romeo, and Juliet responds with the above lines. It's rich with paradoxes because, because while it seems like Juliet is agreeing with her mother, she is actually declaring her love for Romeo.
Juliet says that she won't be satisfied until she beholds Romeo -- dead. Lady Capulet thinks that Juliet literally will be unhappy until Romeo is dead. What Juliet means is that she will never grow tired of Romeo until he is dead.
Then Juliet says that she would temper a poison for Romeo. Lady Capulet thinks that Juliet would engineer the poison to do further damage. But Juliet uses the word "temper" to mean lessen. She wants to weaken the poison, so that all it does is put him to sleep, not death.
The last section is another paradoxical language twist on Juliet's part. She says that it abhors her to hear Romeo's name. Lady Capulet would think that Juliet is so angry at Romeo that hearing his name upsets her. Lady Capulet is correct. It does bother Juliet to hear Romeo's name, because she can't be with him to physically "wreak" her love upon Romeo's body. Shakespeare's audience would have loved that last one. Because not only is it paradoxical, but it's also a huge innuendo.