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)
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.