What you describe is VERY typical behavior for a older bird in a new home and doesn't mean she will be quiet and shy forever. Do you know anything about her background? It is not uncommon for a YNA to have been through 4+ homes by their teen years. Sometimes when you adopt, you never really get a full picture of their background because the prior owner themselves didn't know or was lying to get the bird gone ASAP. Just keep that in mind- if this bird has been passed around, she is probably going to need some extra saint-like patience on your part to come out of her shell and learn to trust again.
Again, I recommend reading the "I love amazons" thread out loud in a soft voice to her. Just pull up a chair near her cage (but not so close she seems uncomfortable) and start there. In time, perhaps bring some nuts (or whatever treat she'll take) while you read and eat (or pretend to eat) yourself while reading/talking to her making a big deal of how yummy it is. Amazons are big winged pigs, she will undoubtedly eventually approach and at that time, slowly move your hand with the treat and let her take it through the bars. That will be your first step in trust building and it will snowball from there. As mentioned, expect a weeks-months long process to win her over and draw her out of her shell. Don't get discouraged, it will happen if you are patient and work on her timeline, not yours.
For now, feed her (within reason) whatever she'll eat. You will, at some point, need to take her to a avian specialized vet to become established as a patient and for a general wellness check. This is essential for new birds to get a baseline of health, but as she doesn't sound to be exhibiting signs of illness currently, isn't old enough to be in the danger zone for certain conditions amazons are prone to with age and poor diet and appears in good condition, so if you wait a few weeks on that, it should be fine. Just don't forget to do it or assume it's not important. You can ask her new vet about specific recommendations based on her health assessment and professional tips to get her to try fruits and veggies. Again, older amazons who refuse to eat healthy food is not uncommon. They are junk food fiends, 'treegulls' lol. Generally switching them to healthier eating habits is an 'extended' process
