It is possible that she's a bit overweight, but if your vet did not bring this to your attention, then I wouldn't worry about it. In the meantime, even though it's making her angry, keep her confined and limited to the floor. It's hard, but it's not forever either. We had to do the same for Miu during his rehabilitation, and for much longer than a few weeks. His new flight feathers kept breaking and he had to be confined for months until they all came in. If you can keep her reasonably content during those 8 weeks, then keep at it.
I think it's more likely that during all her confinements in her previous household, that her breast muscles weakened from lack of use. This is the major drawback to long periods of confinement. It's much like being prevented from walking for similar periods of time. Muscles atrophy and weaken, and when suddenly put to use, they fail to hold you up. The same thing happens with a bird's flight muscles.
Once your vet green-lights flight training, then you can encourage her to flap her wings, but build her up slowly. The trick is to "pin" their toes with your thumb while she is on your hand and encourage flapping in a controlled and limited fashion. Once the bird understands that you are trying to help her, she will be more willing to allow these limitations. Miu, our rescued CAG, used to hang on very tightly and wanted us to hold his feet just as tightly. This enabled him to "fly" by almost dragging us along behind him. It took him a while to build up himself enough to be able to fly independently, but once he was able to, he was supremely pleased with himself and gained much needed confidence in himself.
When we had to retrain our TAG to fly again (after being clipped by his breeder), we encouraged flapping and passed him back and forth between us. As he got stronger and better at it, we'd step back and "toss" him between us, making sure that there was no chance of injury or taking a fall. Having the bed between you is good for this, so if you do happen to miss, the birdy simply bounces on the soft bed surface with no injury.
When dealing with young birds, their enthusiasm can work against what you are trying to accomplish. Learning how to control the situation is always a challenge, but is very important. They are so much like taking on a human child of similar age.