I hope you are right, Kiwibird, but a few years, you said! (S)he is 9 years old, I've had her from a juve. She really took me by surprise, but I am learning about her every day. Thank you for the encouragement!
I bet it is puberty/hormones. A little late, but some individuals are "late bloomers". And yes, parrot puberty lasts a few years. Not that they are satan incarnate for years but they can be a bit unpleasant at times on and off until the hormones settle into an annual cycle. Our BFA was 10 when we adopted him and he was going through the worst of his hormones at that time and he was a bad case. I can attest to the fact if you just stick with them through it, they really do mellow out and come out the other side a nicer bird
I'd guess you'll likely have a far lesser issues with a bird you've had since she was a baby and who's never been mistreated. Also, while the larger "hot 3" (DYH,YNA,BFA) amazons are notorious for hormonal aggression, the smaller guys like YSAs generally do not typically experience extreme puberty/hormonal issues like their larger cousins. Females tend to have fewer aggression issues than males. Be sure she is on a consistent 12 hour sleep/wake cycle, reduce fruit (the sugar!) and up veggies, keep seeds+nuts to a minimum (the fat content), keep an extra close eye on body language, reduce any physical contact (i.e. petting) and if she isn't already, train her to step up to a stick for times she is liable to bite your hand. Stick training is very important with amazons since it is a safe way to transport them when they are in a mood. You should also ignore any overtly sexual behavior. Do not scold her over it as it is perfectly natural/normal but do ignore her- say nothing and literally turn around and leave the room if possible. It may be a natural behavior but you also need to send a clear signal of your disinterest in being the birds mate.