Zenobia is initially immune to damage because she is covered by a wall of tentacles. The player must defeat the tentacles to hurt Zenobia herself. Zenobia will raise her shield again once her health is low. Zenobia will hit the party hard with a physical attack that can knock the player out if not prepared. The battle is finished with a Cinematic Action sequence.
Once Zenobia's protection is gone, the party should switch to Tri-disaster (RAV/RAV/RAV) to build up her stagger meter to 999%. After Zenobia raises the shield again, it is good to switch to a defensive paradigm, like SAB/SAB/MED. After surviving the oncoming assault, the player should return to taking out the tentacles before finishing off Zenobia.