She performed worse than she ever had. The drop-off wasn't gradual, despite poor performances previously... every athlete suffers those pangs. Something snapped.
Nor was the pressure the same before the Olympics. Obviously that's not to say there was no pressure before... there was... but compared to the explosion of pressure of the Olympics it pales into nothing.
As for 'heroic'.... well, I wouldn't say she was heroic, necessarily.
Putting stress on her teammates, no doubt, she did. Nevertheless - - -much better, IMHO, to allow a teammate you know can outscore you have her chance than simply limping thru a performance and denying her teammate the opportunity. - JamesJM