analyst wrote:
to me it looked like she started to fade a little, but then when susan passed her she just completely broke.
In my opinion (which is, admittedly, no more informed than yours) it looked to me like what you described as a fade was already the start of a breakdown. Barringer was already slowing down substantially (and, if memory serves me right, her stride had begun to shorten) when Susan K passed her--and that was, in fact, the reason that Susan K passed her. I think the reason that Barringer went from looking like she was fading for the last few seconds she was leading to looking absolutely broken when she was passed is that Susan K had slowed down for a few seconds (either intentionally to give herself a few seconds to decide whether to take the lead or subconsciously as sometimes happens when you're trailing someone and they're setting the pace) before passing Barringer, and then put in a surge to pass her with authority.
Thus, the image went from Barringer and Susan K running the same pace right before the pass to Susan K blowing Jenny's doors off. This makes me think that there was something physical going on, as Barringer had begun to break before Susan K passed her. This is not to say that a physical ailment or failing could not have been brought on by emotional strain, though.