I raised/rehabbed a phobic BFA female once. She would stress to the point of hyperventilating and almost passing out at the thought of stepping up. YOU NEED TO BE CAREFULL!!!! Phobic behavior, which is what you are describing, is an abnormal fearful/feral reaction that comes on suddenly and if not handled properly will be permanent. This is very different from a change of environment scaring a bird or anything like that, it is an over the top reaction taken place. SOOOO....
NO food outside of the cage, if she gets hungry she will go in to get food.
Stop using your hands for stepping up and remove any jewelery, nail polish.....
Start using your for arms to have her step up, and make sure your hand with it's "scary fingerings" is in a fist.
AVOID DIRECT EYE CONTACT when you are working with her!!!!!
If she runs from your arm (while on top of the cage) back off and just lay your arm on top of the cage and talk to her. When she is comfortable, put your other arm on top of the cage as well, so you form a kind of circle with your arms around her.
continue to talk and praise
Move one or both arms by sliding them (don't raise them off the cage) towards her. Don't make her feel trapped though, so back off as needed.
See if you can touch her this way, but make no move to have her step up. Work on touching toes and such, what ever she will allow.
Once she is comfortable try sliding your arm in front of her feet, but say nothing about it. If she starts to panic, back off and talk to her. If she shows no reaction praise her!
go slow, these steps might take a week or more each. it will depend on her!
Your goal is to have her trust you, and you trust her and to have her step up on your arm, IF she does step up on your arm DO NOT MOVE. don't try to put her in or anything. Just praise her. After a while see if you can slide your arm with her on it to you. If you can and she is fine than do so.
work on all of this first thing in the morning before she has eaten! Even take away the food at night so she will want to go in by her self to eat after your session. After a while she should step up on your arm, and you will slide your arm with her on it towards your chest, once you have accomplished this stand there and talk to her. Your next step will be taken a step or two away from the cage with her, again keep this up till you can walk away from the cage with her on your arm facing your chest. It will take time, just be patient and go at her pace.
Phobic birds are hard. The BFA I helped will never step up again and had to be trained with voice commands, but by doing the above, I could snuggle, hug, pet and play with her like you would a puppy. But stepping up almost killed her a couple of times (seriously). She almost had a couple of heart attacks from it. I do not think your bird is as bad. This BFA was fine, it was one of the birds that I had raised from 3 weeks old. She went to the vet and was never the same. Something happened there. She came back being phobic and missing feathers on her head. Her vet trip destroyed her, but with work she is now living a happy life with voice commands with a person who always takes in disabled birds. I hope this helps!