In case you "forget" again, I told you anyone can have their own interpretations of portrait and this is my interpretation.

XERAMPELINAE(Red clothes)- Ultimecia's ancestor's portrait
VENUS(Love) - Love is what make the world bleed
VIGIL(Watchmen) - The guardian monsters of the castle
INTERVIGILIUM (Sleep) - The sleep magic
JUDICIUM (Judgment) - Alexandria Holy Judgement
IGNUS (Fire) - The Fire magic in the game
VIVIDARIUM (Garden) - The Garden of SeeD
INANDANTIA (Flood) - Leviathan Tidal wave attack
VIATOR (Messenger) - Diablo's dark messenger attack
INAUDAX (Cowardice) - Biggs and Wedge
XIPHIAS (Swordfish) - Gunblade
XYSTUS (Tree-Lined Road) - Fisherman Horizons

Big Picture: In A Garden Sleeps A Messenger:

Diablos sleeps inside the magical lamp which is given in Balamb garden,

See? Anyone can have their own interpretations so your interpretation theory isn't valid so you can't prove Julia= Ultimecia.