Lucetta is Julia's woman in waiting. She functions as a kind of sounding board for Julia, who confides in Lucetta and asks her for advice about romance and love:
But say, Lucetta, now we are alone,
Wouldst thou then counsel me to fall in love?
Ay, madam, so you stumble not unheedfully. (1.2.1-3)
Lucetta seems to give pretty reasonable and grounded advice. Although she can be clever and sassy – she's not afraid to tease Julia about Proteus – we don't see much of her in the play. After she helps Julia disguise herself as a boy in Act 2, Scene 7, we never hear from her again.