I don't think parts* of her story add up, but I am willing to believe it was as a My Nintendo store mess up on their end and/or special set of circumstances.
Her order wasn't cancelled somehow and a code got sent out
Don't codes get sent out day of release, or have they changed that?
The code was active and it downloaded the preload which usually doesn't become available until a week before?
It downloaded an early build or was missing a day 1 update
CS apparently asked if she wanted to keep the code or get a refund, shouldn't it have been refund only?
She's the only person it happened too, or other people have kept quiet