How is Juliet not fickle when she speaks in ambiguous to her mother about Romeo?

In act three scene five, Juliet uses her Words carefully so that her mother doesn't know if she is talking about Romeo or Tybalt. Juliet is weeping at Romeo's departure, but tells her mother that she's not well. Her mother, however, jumps to the conclusion that Juliet is weeping over the death of Tybalt. Thus begins a dialogue in which Lady Capulet speaks of Tybalt but Juliet's replies are about Romeo.

Juliet tells her mother she is not well. Lady Capulet thinks she is talking about Tybalt. "Evermore weeping for your cousin's death? What, wilt thou wash him from his grave with tears..." Juliet replies with "Yet let me weep with such a feeling of loss." Here she doesn't make it known that her feeling of loss is for Romeo and not as much for Tybalt.

Lady Capulet says she was going to send someone to kill Romeo and hopes Juliet will then be happy. Juliet says "Indeed I never shall be satisfied With Romeo till I behold him-dead-". She used the Word 'dead' on purpose so her mother will think dead refers to Romeo. But Juliet uses the Word in reference to her heart. "-Is my poor heart so for a kinsman vexed."

Later in the dialogue, Lady Capulet says"…Thursday morn The County Paris, at St. Peter's Church, Shall happily make thee there a joyful bride." Lady Capulet realizes Juliet wasn't talking about Tybalt at all when she tells her "…I will not marry yet; and when I do, I swear it shall be Romeo…" Her mother then tells her to tell her father and see how he will take it.