It is different with every bird. Take some time every day to just sit by her cage and talk to her without reaching your hand in. Get her used to your sound and smell, and after a few days you can start just be reaching in a little to give her a special treat and leaving your hand in while she eats it. It really depends on how much and what kind of interaction she's had with humans in her life.

The last two winters my Dad has bird-sat his neighbor's budgies, Pixie and Dixie, for a few months while she goes to Florida for the winter. Pixie was always pretty afraid of everyone, but a sign of acceptance and affection from Dixie was she would "attack" you. You knew you are okay with her if she'll come over and peck really quickly right on your fingernail. It is pretty silly, but that's just her!