I had heard about this anecdote a few years ago but it was while googling "Final fantasy invisible woman" that this answer came to me.
Anyway, it motivated me to start over this game that I never finished (never played for more than an hour in fact).
On guard Final Fantasy
The correct answer was Vivienne Westwood! This real-life fashion designer designed the wedding dress used by Lunafreya (the 'moon' in this Limerick) which presumably got destroyed during Leviathan's summoning.
Vivienne Westwood 'exists' as a character in Final Fantasy as NPCs namedrop her when they are gawking at the wedding dress in the shop window, but she does not appear herself as a character model in the game.
Since it is Christmas, I will still let people have a bonus round. Bonus: Anyone can complete this bonus to win a single point. Simply post in this thread before the contest ends.
Here is line one for Limerick Eleven.
When spied some may yell “Giddy!”