Hilda Egglebrecht was the ancestor of Agatha, an elderly resident of the Capital Wasteland. The Soil Stradivarius, which Agatha seeks for the quest Agatha's Song was loaned to Hilda before the Great War. As a talented musician, she was asked to join the artistic and musical elite in Vault 92. During her time in the Vault, she was involved with Parker Livingsteen, the young sound technician operating the recording Sound Lab she regularly played in. She presumably was murdered along with most or all of its residents during the Vault-Tec experiments there (although a laser pistol can be found beside the skeleton near the door, suggesting that they had killed the others and tried to escape via the locked door).
Judging from the logs of her lover, it is likely that Hilda died with him, locked in the Sound Lab when the Vault-Tec white noise experiments drove the residents violently insane, causing the deaths of most of the Vault population and the failure of Vault 92. The prized violin, Soil Stradivarius was left sealed in the Sound Lab, on a table, next to the skeletons of Hilda and her lover.
Hilda Egglebrecht is mentioned in Fallout 3 but appears only in the game as a skeleton.