She's named after the Roman goddess of the moon.
When Kite Tenjo arrived at the top of tower, Diana told Kite to Duel her if he wanted to rescue Lulu. She Fusion Summoned "Penumbral Keeper" and activated its effect to Special Summon a "Keeper Shield Token". When Kite brought out "Galaxy-Eyes Cipher Dragon", Diana activated "Admiration of the Keepers" to negate the effects of "Cipher Dragon", Special Summon two "Keeper Shield Tokens", and force "Cipher Dragon" to attack all "Keeper Shield Tokens" or be destroyed at the end of the Battle Phase. When "Cipher Dragon" destroyed all the "Keeper Shield Tokens", Diana activated the effect of "Penumbral Keeper" to decrease the ATK of "Cipher Dragon" and increase her own LP by 800. As Diana brought the ATK of "Cipher Dragon" down to 600, she wondered if there was any point for it on the field until Kite brought out "Neo Galaxy-Eyes Cipher Dragon". She then watched as Kite took control of "Moon Protector" and Tributed it to bring back the original "Cipher Dragon" with "Galaxy-Eyes Nova". She panicked as both dragons attacked her directly, defeating her.
Diana uses a Deck centered on Fusion Summoning "Penumbral Keeper". Her strategy revolves around creating "Keeper Shield Tokens" through the effects of "Penumbral Keeper" and "Admiration of the Keepers", which prevents "Penumbral Keeper" from being destroyed. With "Admiration of the Keepers" she's capable of nullifying her opponent's ace monsters's effects while forcing them to attack the "Shield Tokens" or they risk getting that monster destroyed, in turn making the opponent's monsters substantially weaker while granting additional benefits for Diana.