I don't think this is finger shyness, since she doesn't seem to be afraid of the finger anywhere else. It sounds like she's refusing to step up in the cage because she wants to stay in the cage.
Is there anything in the cage that she might perceive as a mate? If there is, that's probably the reason she doesn't want to leave, and she might be more willing to come out if you take this object out before you ask her to come out.
Is she exhibiting any nesting behavior, like tearing up the cage paper or sitting on the floor in the corner? Hormone reduction techniques might help in that case.
Do you take her out of the cage every day or is it less frequent than that? A bird that doesn't get out too often may be reluctant to leave the cage at all. The solution to that is to let her out more frequently.
In any case, you want to make sure she has fun while she's out of the cage so she'll start wanting to come out. I usually recommend food bribery, but since she's not accepting treats from you right now you'll have to figure out a different way to entertain her, for example some kind of toy that she really likes.
If there's a special food she likes (millet spray for example) she can gradually learn to take this treat from your hand. There's an article on food bribery at
http://talkcockatiels.com/showthread.php?t=28661 that I posted on another board. It's aimed at cockatiels but the same technique will work for budgies.