Clearly, Shakespeare's Nurse is a character designed for Romantic comedy, and with her exit begins the tragedy. In Act II, Scene 5, the Nurse is presented as the loquacious messenger, who delays what Juliet expects to be the "wind-swift dispatch" of Cupid. This contrast between the demand for the message and the prolix ramblings of the inarticulate messenger who is "unwieldy, slow, heavy, and pale as lead" (2.5.17) is what creates the comic relief.
Her effusive outpourings about her aches and pains are ridiculous in contrast to what Juliet considers urgent: whether Romeo has responded to her message. Clearly, the Nurse enjoys tormenting Juliet in her youthful passion.
Jesu, what haste! Can you not stay awhile?
Do you not see that I am out of breath? (2.3.29-30)
It seems, also, that the Nurse does not consider the seriousness of Juliet's being in love with an enemy of the family, for she makes no mention of this fact, nor does she attempt to give any advice to Juliet as an older relative would probably do. Instead, she rambles on and banters with Juliet to her own amusement until, exhausted by her own loquacious selfishness --
Beshrew your heart for sending me about
To catch my death with jaunting up and down! (2.5.52-54)
she reports Romeo's message that he waits for her at the cell of Friar Laurence.