The First Battle: will have Zeal spam Halation - Sets HP to 1 many times, sometimes twice in a row. Be careful, as getting hit with her default energy spheres, despite doing little damage, will still KO a character. If Frog or Ayla are in the team, Frog Squash, Dino Tail, or team techs that has both of those moves in them combined should do maximum damage and finish her off very quickly, if you wish to defeat her quickly yet risky. Otherwise, having someone who heals all would be recommended while others do damage.
The Second Battle (after Mammon Machine): If Magus is in battle, his music plays. Otherwise, the boss 2 track plays. Zeal splits into 3 parts: The 2 hands and the face. Attacking her hands should be avoided, as it will provoke threatening counter attacks that will either drain HP to 1 or drain all of MP to the attacker, thus making all techs that hit all avoided in this battle. Attacking her face is the goal here. Starburst, while rarely used, is her most powerful spell (water) that hits all; Blue Plates and Blue Vest are recommended equips to heal. Pay attention to her HP. When exactly 10,000 HP of damage is dealt, her next set of moves (in order, EXCLUSIVE to this scripted trigger, and used once) will be:
Halation. Heal your party immediately OR kill her fast enough.
MP Buster. Whoever selected the triggered blow from their menu (single or mult-tech) gets hit with it. Either replenish MP or expect to use regular attacks throughout the entire battle for that character.
When the face is destroyed, so are the hands.
Ayla is heavily recommended in this battle due to charm and is recommended to fight this battle 3 times. The Prismatic Helm and Prismatic Dress are the most powerful equips in the game outside the DS remake. Just be fully aware to backup Ayla once the hands' counter attacks will shave her HP to 1 and drain all of her MP.