i swear her problem is that she is kicking herself, literally. her left foot comes forward and hits her right calf, then she loses her balance and dives. there MAY have been contact from behind, brushing mcgee's right knee, but it was the swing forward where she hits her own calf that made her trip.
the EXACT same thing happened in london. her left foot brushes aregawi's right knee possibly and when she swings that leg back forward her left foot hits her right calf and she trips herself.
people hit their foot on their opposite calf all the time. you see the telltale mud marks in xc. but it's usually the less talented athletes.
uceny is physically off balance (yet still an incredible specimen, obviously). she has her head constantly cocked to the right side. if you looked at her from above, and considered straight ahead 12:00 and straight back 6:00, it's as if her head is pointed towards 12:30. you can see she leads with her left eye ahead of her right, almost with a protective/defensive look on her face.
her left lower leg has the tendency to want to swing towards 12:30 because her skull is positioned in that orientation, as if that is straight ahead, and that is why she keep kicking herself when she is barely bumped, but ONLY with the left foot hitting the right calf. her right foot will want to swing slightly off to the right as well, but that means it will be well clear of her left calf.
she needs to get her head on straight, literally! it's not psychological, it's structural. and it's not bad luck, getting bumped is part of racing. crazy though it may sound, i think she'd be well served training with a patch over her left eye for a few sessions at least, which would naturally make her right eye "lead" and cause her to orient her head towards 12:00.