She is a witch who goes around claiming to be related to various families as a "great aunt", and then ages their children into senior citizens with enchanted prune cookies to marry them off to her friends, including Lillian and Mimi, for a price. When Tom threw a pitcher of prune juice at her, her face melted away to reveal a skull, then her whole body collapsed into dust.
She also appeared as an enemy in Goosebumps: The Game. She's defeated the same way as the book with prune juice. Once she's defeated, the player must take the cassette tape she leaves behind.
- Aunt Dahlia is one the very few Tales to Give You Goosebumps monsters to appear in a videogame.