Having just read through the whole thread... I'm at a bit of a loss as to what to tell you.
Does your friend have the same problems that set her back at shows riding at home? In lessons? I gather that you both work with an instructor... do she and the instructor focus on improving her problem areas in lessons? I get "forgetting" details in the show ring with all the fuss about remembering your pattern, etc., but the only way to improve her equitation is consciously practice riding with perfect equitation at home. If she replaces her "bad" position/curb rein habits with good equitation through actively working on those habits in lessons and home riding, the correct way will become the natural way, and not be one more thing to remember in the ring. If there is an actual memory problem at work (possible, but I doubt it... eq and rein control is muscle memory, not mental memory in my books), fish is supposed to be good, as well as a few other natural "brain foods." Give it a Google.
However, the only thing that will help your friend "break through" is actively targeting her faults in practice/lessons and improving them before entering the ring. If it's a problem at home, the show atmosphere isn't going to make it better.
From the sound of it, she has every advantage in this -- years of practical experience, an instructor/trainer to work with (whom I assume from the previous posts is quite qualified), a horse that has been proven to be able and successful under other riders (and is even of a preferred color... no comment there), the wherewithal to actively pursue showing opportunities that are "no local 4h pony club kinda thing," and knowledge of what her eq faults are and what to work on in order to do better. The ball is in her court.
A stubborn horse walks behind you, an impatient one in front of you, but a noble companion walks beside you ~ Unknown