Probably because "Scamco" (as the company is sometimes called on GAF 
) had the foresight to know that they were going to do something with that character/concept any way, it was more of a thing of just a matter of time and how they were going to implement her.
Somehow, I don't think that's it. I imagine the game wasn't as finished as it could have been. Look at the PS2 version of Symphonia versus the Gamecube one and the amount of differences there. Of course, if this is stemming from GAF logic (or lack thereof), I'm not surprised and will largely ignore it.
Here's the thing... I don't see how the hell she'll fit into the game aside from being another mostly useless child character (never been a fan of them... this includes Presea [too slow], Anise [too chirpy], and Karol [too slow and chirpy.] I'm hoping we can at least get that mary-sue, Flynn, in the party instead. He seems to have the potential to be a much more lethal fighter if he had a larger move pool (this is drawing from his move pool as a boss, not when you play as him in that one event.) He seems to be similar to how Asch fought in Abyss, where he was based of the Magic Swordsman class. Perhaps giving him a few spells and some of the traditional Tales of moves (Lightning Tiger Blade? Hell Fire?) will help?
Also, someone needs to have Indignation as a mystic arte. I'm calling either Rita or Judith.