1. She's lowbrow. The nurse is a working class, bawdy character who makes comments and jokes at Juliet's expense. Her sexual undertones are inappropriate for a woman in charge of a young woman, yet she seems oblivious to this.
2. She's indiscrete. She tells too much, and ignores lady Capulet's and Juliet's request that she hold her tongue (1 iii). She tells Romeo that Juliet has another suitor who "would fain lay knife aboard" (wants to have sex with her) when there is no reason for her to reveal that info.
3. She is well-intentioned, but foolish. She seems concerned about Romeo's integrity, telling him it would be weak dealing if he were leading Juliet into a fool's paradise, yet in almost the next breath she's arranged to help Romeo hang a ladder to Juliet's bedroom.
3. Drama Queen (see the exchange between her and Juliet after she first sees Romeo)
4. She is pragmatic. When it looks as if things won't work out with Romeo, she counsels Juliet to take the second choice (Paris).