The final member, and perhaps the most difficult, Goddess can use a basic attack, Hit (basic attack +50%), Thundara, Thundaga, Flash Rain, Quasar, Lullaby, Entice, Overture (an occasional counter; makes your other allies' hit the targeted character), and Cloudy Heaven (only used after being hurt eight times late in the fight; gives Doom to all, and forces them into a Zombie upon dying, which Reraise DOES NOT HELP AGAINST).
Get ready for hell. Start off with Hastega and Mighty Guard. You'll want to probably focus on physical attacks, preferably NOT a basic Attack, as that may induce Overture. Everything else is cool. Those focusing on the physical attacks will relish Valor; I'd prefer to keep everyone else on a healing duty.
Of course, probably your biggest question is how the hell to deal with Cloudy Heaven. There are but two solutions. One: have Zombie-immunizing equipment on and use Reraise (or also have Death-immunizing equipment). Two: if you lack that stuff, quickly kill someone (won't induce Zombie; only Doom-death will) and use Arise (preferably). Your offense will tend to remain the same throughout the fight, though.
After winning, you'll get a message. Anyways, use the nearby Save Point. Go north... See that switch? Use it and you'll be dragged into the final series of battles. Save, save again, and save a third time to make sure you have a back-up. Heal and place great equipment on everyone. You ready? Let's finish this!