Solution
A Treat-Napping
When both Ella and Don claim to be the one signing for the kit’s delivery… Mogau knew one must be lying.
Ella says she put the kit into the freezer and Don tells us that she left the box on the counter for an hour. But according to the image of Ike’s delivery that he sent to Ken, the kit explicitly required that it had to be “kept frozen”.
If Don intended to play fair in the competition, she would never have left the box out on the counter to melt in the first place. But she knew better than that. Don did put the box in the freezer… in her apartment during her lunch break.
…And so, Don is the treat-napper!