How does the Nurse feel about Juliet? How do you know this?

The nurse loves, respects and protects Juliet like a mentor.

Throughout the play, the Nurse jokes about Juliet (remembering how Juliet fell forward as a child and how Juliet was weaned off of breastfeeding), teases her (won't tell her what Romeo said), and tries to stay right inbetween parent and friend (she knows about Romeo but waits a few scenes before she will encourage Juliet to forget about him).

You can believe each of these by reading the Nurse's and Juliet's conversations in Act II, scene v, and later in Act III, scene ii, and finally in Act IV when Juliet's parents want her to marry Paris.