A person should help the people they care about.
"Your lady mother is coming to your chamber. The day is broke; be wary, look about." (1064, 40-41)
The Nurse is speaking to Juliet because her mother is on her way to Juliet's room. Romeo had stayed with Juliet over the night, and if he had been caught by Juliet's mom, the consequences for both Romeo and Juliet would've been detrimental. The nurse was caring for Juliet by warning her and Juliet of the oncoming threat.
"I am aweary, give me awhile. Fie, how my bones ache! What a jaunce have I had!" (1038, 26-27)
The Nurse is talking to Juliet to report on the wedding plans. The is old and she is still running around for Juliet trying to get as much information as she can for Juliet, forgetting the pain she is going through for Juliet's sake.