No their bites are not quite that bad, yes they can bring blood but I don't think they would split a finger open, they could crush an english walnut but that is only if they can get their beak around it but I doubt they could crush a black walnut as they are too hard, now your macaws are a different story altogether.
If you show fear she will pick up on that and then she will bite you for sure, you need to not be afraid and when the time comes to try to have her step up then you offer the back of your hand balled up into a fist, she won't be able to get a good hold on the skin because it will be tight. You may just have to suffer a few bites for her to learn you are not going away.
Please read and reread Dave007's post as he is very knowledgeable in greys and their behavior, if anyone here knows it is him, he won't steer you wrong.
BTW, what is her name?