Well she definitely was supposed to be the Final Aeon as Yunalesca was the one who changed her to the Fayth. And well she wanted to give her son power to protect himself and she was dying anyway (I guess from some kind of disease?) as when the party see her and little Seymour in Zanarkand she says something among these lines: "I don't have much time left". BTW even Final Aeons DO have statues as we can see the chamber before Yunalesca had Lord Zaen or w/e his name was statue, just without his soul (probably because he merged with sin and was killed long time ago).