Not saying what she did was the right thing to do, but I don’t see the two events as similar, to be honest. Calvin wilfully kept going after his horse went down, whereas Emily just tried her best not to fall off and inadvertently spurred the horse. I would understand less if this happened in the cross country portion, but as it was showjumping, the last phase, and potentially the horse’s last event at this caliber, I view it more as she tried her best to stay on to complete the course and therefore be noted as completing the event.
Personally, if I was jumped loose at speed, I’d probably try my best to stay on too - it would be instinct, no? I’d have to fight to let myself drop.