One of my birds is a rescue (Jimmy) who was sick when we adopted him. We had to take him to the vet 15+ times before they found the cause. The good news is he is healthy now but the bad news is that because every vet tech or vet that has ever handled him has been a woman, he now is very fearful and aggressive toward women (whereas he used to step up for me before we initially took him to the vet).
I have started clicker training with him to work on tameness but I don't trust him with my hands (he draws blood) at this point. He isn't a big bird (he's a brown-headed parrot)
but when he bites he latches on and won't let go. My solution is to either give him bites of a long sprig of millet as a treat or to put small bits of his favorite treat (walnuts) into a measuring cup with a handle. He can eat the treat out of the cup without me having to worry about being bitten.Maybe you could try this with Pookie, at least for now? It's very important that you don't put yourself in the position where you are being bitten or lunged at in the first place (if you can help it) because it damages your relationship with the bird. You also want the bird to be in a good mood during training so if she's growling at you and getting aggressive the entire experience could be counter-productive.
If the only problem you have right now is your fingers then don't introduce them yet. If she's mastered targetting you could try to build more trust with her first by teaching her another trick or two (waving, turning around, ringing a bell, etc.) before you let her near your fingers.
Alternately you could slowly use the targetting to teach her not to bite your hands. This is my plan with Jimmy: I am target training him night now and after he's mastered that my plan is to slowly "target" him closer and closer to my hand. I'm not going to even try feeding him from my hand until I can get him to either step up or stand near my hand without any signs of aggression or fear.
Another method to accomplish the same thing is to place your hand as close as you can to the bird without her lunging or biting. You then click and reward the bird for basically tolerating the presence of your hand without becoming aggressive. Over time you move your hand closer and closer and eventually you introduce the bird to touching.
Not sure if this will help but hopefully it will.
Best of luck to you and Pookie! I love that name; growing up I had a Quaker parrot named Pookie. 
