She is, by far, the strongest opponent you face in Mk II
: you even get a Gold Trophy if you can overcome her might.
It's possible that, after peforming whatever acts she did prior to the game's events, she left her role for another goddess to fill while she faded into obscurity. Ages later, she is challenged by Nepgear and her friends, seeking to prove their strength against a powerful force.
...huh: it sounded much better in my head. Go figure.