Congrats on your new amazon. White fronts are one of the smaller zons known for a generally sweet disposition (as opposed to some of the larger 'feistier' zons).Unlike dogs and cats, parrots are not domesticated animals and are very shy/timid/fearful until they learn different. She is acting perfectly normal and with proper training/socialization should be a wonderful companion in no time
Since she is so young, this is her first home and has no experience with training and no prior traumas in her life (like some older rescues), I strongly suggest you look into positive reinforcement based training, starting with target training right away. I really wish we knew about it when we adopted our bird, it would have made training and socializing him MUCH easier! Plenty of free youtube videos on the subject as well as DVDS and books you can buy. I *personally* like Michael Sahzin, aka "The parrot wizard". Even my slightly stubborn 16 y/o amazon picked up on some of his basic trick training methods rather easily. I *personally* feel he presents the concepts in an easy and fun way, though there are many trainers and everyone finds different teaching techniques of the same concept easier to follow

. I suggest you start looking into different well known bird trainers and see who you really "connect" with and follow their program. Some are very technical, using more dry scientific terminology in their presentation of concepts, whereas others present the same concepts in more 'layman's terms and are a little more 'fun'. I would also suggest until you have started making progress that you stop feeding from your mouth. An amazon can inflict a very nasty bite, and better a finger than your lip! Keep her off your shoulders too until you can trust her to step on your hand reliably, has been bite pressure trained and you see she's really warmed up to you. Even if she seems to want to be up there,
being on your shoulder is a privilege for trustworthy, gentle birds. For now, I would focus on target training and trust building. Food is a good way to build trust, so have your son sit by her cage and talk to her (or even review his homework out loud, it's not like it matters what he's saying!) in a soothing voice and offering treats when she comes over close to him willingly. Best of luck, and remember to have patience!
Edit: one last thing, there are quite a few young bird owners on here, so it might be nice for your son to get involved on the forum too, seeing as he will have this bird for the rest of his life! It's always nice to have a community of like minded people to help support you, especially at such a young age taking on a big responsibility like a parrot who has the intelligence of a small child! I wasn't much older when I adopted my zon (19) and I joined this forum a few years later. It's nice to be able to ask whats normal, how to do things, general advice, vent frustrations ext... It would have been even better if I had been on here from the day I brought him home, may have made those initial few years go better (he was already 10 y/o and on his 3rd home by the time I got him though, not exactly a clean slate like a baby bird).