It think it would make sense, if she created him from squall in the game's main timeline, then the hundred years or however far it was in the future that Ultimacia came from Griever was by that time a legendary GF. Then when she returns to fight that battle again from the future, it says "Legendary GF".

That may not be exactly what you meant though. It gets a little confusing trying to sort this one out. Let me know.