You have to push her, only way she overcome it, as dealt with birds that are way to aggressive and waiting sometime don't work as some birds are use to being cage bound and scared of hands and won't accept treats, or target training easy. There are other methods that we use at the rescue to rehabilitate birds that have behavior issues, I leave that out for now, unless methods of positive reinforcements doesn't work. Just don't ever chase bird around, or get to aggressive as you can lose trust and be harder to regain it back. Target training is best way to get started, but you likely have to get her away from cage as it consider her safe spot and she likely won't want to listen and will have cage aggression. It best to get her to a different room on T stand for training sessions some way. Birds are more willing to step up when they are on the floor it also a trick you can use to get her away from cage, if bird use to being cage bound, or just way to aggressive. You can also use her perch she familiar with to get her to step up on it. Try not to show fear, or stop if she bite, if you give in, she learn that biting is a way to get her way and will be more willing bite more, but also give a break every so often.
MMM....See I disagree with this a bit...Yes, maybe in a "baby steps" way, but PUSHING (as people often do) can cause a bird to turn away even more....It depends on why the bird is aggressive, but pushing a scared bird will only harm the relationship, In my experience, building that relationship and trust is key (and not rushing things....keeping things positive and not locking the bird up).
It case by case dealing with a caged aggressive bird, or scared of hands as was a pet-smart bird is way different then dealing with a bird your just trying to bond with and adapted. Like Pepper my cockatiel feared my hands and you could leave millet and he won't dare go near it, as he also was a pet store bird and kids use to go into enclosure and grab him at random. I opened the cage waited till he was out leaving the room as he would never step up and then once he was away from cage I was able to get him to step up even through he was still scared, but didn't bite and stay on and then made a habit of doing this till he step on without have to wait till he was out of cage and did on his own. Then he bonded to me fully afterwards. I had to push him and did it without having to be to aggressive. It only took me 3 weeks to tame him.
If I waited till he was fully ready to, it would have taken months and years and reason you see so many untamed birds on craigslist. I use to dealing with aggressive birds that have behavior issues and it pretty much different from bird to bird. Same method doesn't always work.
Baby when harness training her, she hated it at first and I showed it to her and even let her play with it, but as soon as you tried to loop it on her she would go into bite mode. The trick is I didn't give in and I didn't stop I just adapted and found away around and used the larger loop so she won't get tangle worst case and worst case I would get bit. To my surprise it was her bluff bite as I refer to it as and she allow it to be looped after 4 attempts give her a break for a few minutes in-between, then second day was able to get it fully on her correctly and using the head loop this time and rewarded her and took her outside for a couple of hours to get her use to the harness as she would pick at it and outside magically she forgot it was even on. 3rd day she put her wing out and help me put it on her, she realized I guess it meant going outside. If you give in to your bird that same training could take a year, You have to learn when to call their bluffs and not give in is key without getting to aggressive, there is a fine balance and every bird is a different approach.
Never lock the bird up, if anything get that bird away from the cage as likely cage aggression. Train bird in different room altogether using a t stand as guy above shows in video.