Whom would you consider in the story as a foil to the Capulet family nurse?
A foil is a character that contrasts with another character and so highlights various facets of the main character's personality.
Well, I think a foil can also be someone similar to the main character in certain ways, that is, in some key way, a reflection of them. Otherwise, for example, the Prince would be a good foil to the nurse - he's nothing like her, he's in control, unlike her, ... you get my point.
I think the best foil - and the most obvious "pair" with the Nurse - is Friar Laurence. Why?
Firstly, because the two of them are crucially the only understanding adults in the play: both of them are the generation above Romeo and Juliet. They are, moreover, the only two adults who are entrusted (by Romeo and Juliet) respectively with the information about their love and marriage.
Both of them provide advice which is then followed, and both of them actually interfere with the course of events: the Friar actually performs the marriage ceremony, and the Nurse carries messages between Romeo and Juliet.
And lastly, in the event of everything going wrong, both of them eventually resort to cowardly, backing-out-of-it advice. Here's the Nurse:
I think it best you married with the County.
O, he's a lovely gentleman!
Romeo's a dishclout to him.
And here's Friar Laurence:
Come, I'll dispose of thee
Among a sisterhood of holy nuns.
Stay not to question...
There's even a moment when Shakespeare mirrors the two characters explicitly:
Where is my lady's lord, where's Romeo?
There on the ground, with his own tears made drunk.
O, he is even in my mistress’ case,
Just in her case!
Within the confines that you have stated, Benvolio of "Romeo and Juliet" acts as a foil to the Nurse since he is usually the voice of reason for Romeo whereas the Nurse is rather comical and foolish, providing some of the comic relief in the play and encouraging Romeo in his impetuous love for Juliet.
For instance, Benvolio in Act I advises Romeo to not rush things:
"Be ruled by me, forget to think of her [Rosaline]...Examine other beauties" (I,i, 190,194),
while the Nurse encourages Romeo in his attraction to Juliet:
"I tell you, he that can lay hold of her/Shall have the chinks [money]" (I, v,112)
Further evidence that the Nurse is not reasonable like Benvolio comes later in the play when she advises Juliet to marry Paris when she knows full well that Juliet has already married Romeo.
Well let's see here...I'd have to say...Juliet...I can't really think of any character that has a characteristic that sticks out like a sore thumb: The misuse of time that comes from irrationality, thinking before acting. If you haven't already seen symbolism in the Nurse's lines in the beginning acts, you're kinda missing out on a lot. The nurse gets time right. Aside from Benvolio, every stinkin' character gets time wrong, even the Friar, Romeo, and Juliet.?
The misuse of time is a huge thing throughout Romeo and Juliet. From beginning to end, characters literally screw up time, except for Benvolio and the Nurse. They may go along with things, but they always have this feeling that something might be wrong.
I really wish I had my book handy...I can't come up with any quotes...
I don't know if irrationality is the right word, but all the characters do things without thinking and that's killing them literally. Except for Benvolio and the Nurse.
There could be other ways to look at this, but I choose to look at it as a motif of time kinda thing...