With her bumbling mannerisms and rather risque speech at times, the Nurse is a comic figure; as such her speeches are often interjected into serious scenes in order to provide comic relief.  When, for instance, Romeo inquires of her who the fair maiden is at the masquerade, the Nurse provides added commentary to her response, saying that she has nursed the girl and whoever "can lay hold of her/Shall have the chinks" (1.5.124), not realizing that she is talking with a Montague. 

Later in Act II, Scene 5, when the Nurse returns to Juliet with the message from Romeo, she is delays this message by complaining of her aches and fatigue instead.  While she may be reluctant for her cherished Juliet to be in love and want to marry Romeo, the Nurse is probably just being the Nurse.  For, this delay and her circumlocution is consistent with ther character.  After all, she jokes with Juliet and even makes innuendos later about Juliet's possible pregnancy.