Definition of Imagery
As Latinus and Amata attempt to convince Turnus to surrender at the start of Book 12, the reader gets a rare glimpse at Lavinia. With a combination of imagery and simile, Virgil describes the character's pure, innocent beauty.
In most of the Aeneid, Lavinia is merely mentioned in prophecies and in passing. She briefly appears in Book 7, when her hair catches fire as she lights an altar. The narrator states that prophets treat this as a sign of "a brilliant fame to come" and a portent of "a long, grueling war." Lavinia's flaming hair can also be interpreted as a representation of the role she comes to play in the war. While the conflict rages around her, the young girl plays no active role in its blaze.
Just as Helen is often blamed for the Trojan War, the narrator occasionally suggests that the war between the Latins and the Trojans is Lavinia's fault, like when he in Book 11 describes her as the "cause of all their grief." However, the description that the reader gets of Lavinia in Book 12 indicates that she's passive in this culpability:
As Lavinia heard
her mother’s pleas, her warm cheeks bathed in tears,
a blush flamed up and infused her glowing features.
As crimson as Indian ivory stained with ruddy dye
or white lilies aglow in a host of scarlet roses,
so mixed the hues that lit the young girl’s face.
Besides emphasizing Lavinia's beauty, the imagery and simile in this passage characterize her as a timid, passive young girl. The whiteness of Lavinia's skin represents her innocence; even a mere blush poses an interruption to her silent sanctity. In contrast to Helen, who arguably plays a more active role in the conflict between the Spartans and the Trojans, this description shows that Lavinia has minimal agency—she doesn't even seem to possess a voice of her own.
Hardly making Lavinia come alive as a fully fledged character, this description undergirds her lack of real characterization or character development in the poem. Despite technically existing at the heart of the conflict, she's inactive like a piece of ivory and fragile like a group of lilies. Ultimately, Aeneas and Turnus aren't fighting over Lavinia, but over the future of Italy. The young girl can be seen as a sort of alibi for the war.