Here's what my brother says, with a couple minor edits and paragraphs added for convenience:
"For the most part, what [Neshomeh] said was true. Footwork is easily the most important aspect of fencing to hone. If your footwork is good enough, you can participate with little to no experience in any of the three weapons and perform well.
"The real reason footwork is crucial is distance. If you are half an inch too close they hit you, half an inch too far and you miss them. Precise control takes a lot of strength at those speeds and learning how to control not only how close you are to them, but how close you allow them to come to you is half the game. Getting just close enough so they think they can attack safely, then being just out of reach, is the best way to set up a winning attack. And, as Mr. Miyagi says, the best way to avoid an attack is to not be there.
"As long as [you aren't] going to attempt to have this person do any significant amount of fencing in the story, there are a few nice hints that I can describe that will make the character seem more believable. First off, not only does a fencer's legs have to be very strong, they become asymmetrical after a while. Your front leg (right for most people) will have much larger quadriceps than your left and the left calf ends up looking like someone's fist embedded in the back of your leg. This is avoidable with exercise, but it's something unique to fencers that [you] could bring up and impress any real fencers who might be reading.
"[Your] question of forms is based on Eastern martial traditions, kata and so forth. However, [you] could impart a certain character to Amy's fencing fairly easily. Each weapon has a very distinct style, too, and within that the best countries in fencing tend to have their own unique personalities: Russians fence in a very direct and simple way, the Italians flourish and spin their blades more dramatically, and the French are just [darned] irritating. Americans are usually heavily influenced by the older styles as their coaches tend to be immigrants from another country.
"Saber is incredibly quick; each action happens in the course of a few seconds and entire bouts are resolved in less than 3 minutes. Foil is more drawn-out and complex, usually involving both fencers moving from one end of the strip to the other a couple times before any touch is scored. Then épée is much slower-paced, but no less intense in its own respects. The fencers stand off against each other, generally they hop a little bit the whole time, it's similar to a tennis player rocking back and forth so they can respond instantly. A friend of mine has the nickname "Proud Baby Mudfoot" for not doing this.
"During this process, each fencer is looking for a weakness in either their opponent's form so as to attack at an angle that they can strike without being hit themselves (the whole body is valid target in épée), or in their opponent's rhythm. If you can attack whilst your opponent is mid-step/hop or immediately before they do, so as to surprise them, they'll usually just kind of stare blankly at you while you poke them indiscriminately.
"So there are a lot of options [you] can go with as far as what [you want] the character to be like and how potentially real combat would end for her. Speaking of real combat, if [you intend] to use their fencing to actually fight other humans to the death, or the severely wounded at least, there are things that are important for [you] to know. First off, the reason right of way exists is actually to train a person for real combat. The reason you score when you do is to teach you that you need to defend when attacked and attack so as not to be skewered in the process. If they attack and hit you, and you counter-attacked, they get the point because you were dumb and made no effort to defend yourself. If you attack and are parried, odds are they can attack you before you can recover, and if you try and attack again and they hit you, they get the point because you were stupid.
"Épée does not have right of way; it's a common misconception that épée is the most realistic because the entire body is valid target and you use the largest blades. Rapiers are very well balanced and quite bendy actually, which is good because if they were too brittle they'd break all the time. Épée was actually training for first blood duels with the goal being simply to touch your opponent first and draw blood to win. If you attacked at the same time and both drew blood there is no clear winner and you continue the match. The exception of course being if one of you is dead and the other isn't.
"Saber was set up as training for cavalry troops fighting each other on horseback. Saber has changed the most in its history and in that respect it is virtually useless, but fighting on foot it isn't as bad though, it's the fastest and it's the only one that features cutting attacks. The target areas are set up to teach fighting for maximum effect. Aiming for the body is the most consistent way of scoring a lethal blow. Limbs move about quickly and unpredictably, people are very wary of their heads and can move them side to side very effectively. Watch a high level boxing match and you'll see what I mean. Torsos are big and the hardest part of one's self to get out of harm's way. There are lots of squishy bits that aren't protected by hard bones for your blade to graze off of. Those squishy bits are also pretty important for people to survive; puncturing lungs, hearts, or stomachs will generally kill if they aren't treated by very advanced medicine very quickly.
"How Amy would deal with brutal fighting depends on her level of dorkiness and/or general ferocity. Judging by what I've read, she would just die. Without deliberate practice for the purpose of really fighting, all she could rely on would be her footwork and sense of timing, which are really important and would let her dance circles around any one moron with a baseball bat. If she went up against someone with martial weapons training or a group of people, she'd just get smoked. It takes a special kind of dork to work on learning the martial applications of fencing alongside the sporting aspects. Generally speaking, people who achieve an A ranking aren't dorks, they are athletes. I'm a very rare exception and I wasn't as great a fencer as I could have been for it.
"If either of you have more questions I can answer them.
"Oh, speaking as a fencer with anxiety, there are things that would be likely for Amy. She would be a defensive fencer. She would lose in saber. Saber is entirely too aggressive for someone with any apprehension at all to succeed in. Of course there's levels of savantism or whatever, [you] could write it off in a lot of different ways, but speaking from experience she would perform ideally in épée or foil. Being taller or shorter would significantly influence her style as well."
That should really help. My brother is a cool dude. ^_^
~Neshomeh