The original writer of the lines.
Could be, but I think it is less likely than another person doing a quick run-through of other “first lady” speeches. It’s something anyone might do if they had no idea where to start and it’s perfectly okay for getting ideas. There was just a bit too much copying and not enough disguising.
The author herself probably knows the Michelle speech by heart and recites it to herself every once in a while. Very unlikely she would repeat her own words.