Don't reward the screaming. Always do a subtle check to make sure she's not screaming for a valid reaon...but otherwise ignore her.
If you do have to interact with her while she's screaming, try whispering to her. Hopefully she'll stop screaming to hear what you're saying. When she's quiet...reward her.
I find that all my birds need time. Don't push her to do too much too soon.
My guy was very quiet when we got him (10 weeks old). He was like a parrot statue. But it didn't take him too long to settle in. I'd say by the time he was 5 months old he was doing really well. He startles a bit easier than the Amazon, but not as bad as the AG...
Also, don't over react to their reactions. They take their cue (whether to be calm or excited) from the rest of the flock. If you stay calm and steady, they're more likely to be calm and steady. It's a form of modelling.
...works with dogs, kids and horses too...
Every parrot has a duty: To reduce the world to toothpicks.