The Nurse certainly functions as a confidant and mentor to Juliet for the majority of the play. During Act III, after Juliet and her parents fight about her marrying Paris or not, the Nurse offers some really good advice, although Juliet doesn't actually take it. The Nurse says:
Romeo is banish'd; and all the world to nothing,
That he dares ne'er come back to challenge you;
Or, if he do, it needs must be by stealth.
Then, since the case so stands as now it doth,
I think it best you married with the county.
O, he's a lovely gentleman!
Essentially, the Nurse is encouraging Juliet to marry Paris instead and cut her losses with Romeo. What makes this particularly motherly is the fact that it is good advice, and in true teenage daughter form, Juliet will ignore it.
Earlier, in Act I, the Nurse is trying to remember Juliet's age. In determining it for sure, the Nurse goes down memory lane. She remembers what it took to get Juliet to stop nursing and she remembers Juliet trying to walk. Only a mother remembers those types of moments and scene 3 demonstrates that the Nurse helped mother those moments.