It's not surprising the ban starts at a date earlier than when she was caught, the UCI strongly believe she was using the motor earlier.
For example, the ability to bunny hop varies. http://www.cxmagazine.com/to-hop-or-not-bunny-hopping-cycloc... claims that, in Sven Nijs's case, it is to do with his BMX experience.
I couldn't find a good video from cycle-cross, but here is a nice example from road racing: https://www.youtube.com/watch?v=iPHnqI13vPk. Not everybody is as willing to take those risks and as good in recovering from (for him) minor mishaps as Vincenzo Nibali. Some cyclists are even known to take in a few bisons of water at tops of mountains because heavier bikes descend faster.
(I don't say that because I buy the story about the friend, it's just a plausible reason to keep it hidden)
On the flip side, if the bike was actually a friend's bike, what do you say to that friend that got you banned?
She admits that it WAS her bike. But that she sold her bike to a friend who then installed a motor, brought it to her event, then her "helpers" mistakenly brought it out to the pit area.
See, her original explanation that it was just a friend's random bike didn't wash with it being painted like her other race bikes are. This new explanation of it being one of her bikes that she sold to a friend, now fits in with the narrative she is trying to spin.
Honestly the whole story is nonsense.