It should be obvious, but Drusilla was based on Claudia, except reversed (woman driven mad with the mind of a child instead of a child driven mad with the mind of a woman). A whole slew of Buffyverse characters were based on Anne Rice's archetypes.
Tribute to l'enfant terrible herself, Claudia.
For those unaware, Claudia was based on Anne Rice's own daughter Michele, who died at five years old from leukemia. The resulting depression led to Anne Rice publishing her first of many gothic horror novels, starting with Interview with the Vampire, in 1976. While Claudia was based on Michele, so was Lestat on her husband Stan (originally intended to be named Lestan) and Louis on herself.
The 1976 novel is unfortunately the only entry in The Vampire Chronicles from Louis' POV, which came from a place of her own personal trauma. Lestat was obviously a far more flamboyant, fun, fanciable character for her to focus on, but ultimately not as prone to exploring the existential crises and philosophical questioning present in her original novel.
One may also notice that the doll shop owner Madeleine's backstory is that of a mother who lost a young daughter who likewise never got to grow up. Rice's house in New Orleans was famously filled with antique dolls, which is imagery very much associated with Claudia.
For obvious reasons, a five year old was deemed unable to handle the demanding role of Claudia, which is that of a woman's mind driven mad trapped in a child's body (she's actually over eighty years old by the end of her story), and so the role was aged up for a then eleven-year-old Kirsten Dunst. There was a nationwide search that included younger actresses, but Dunst was one of the few who could handle the part. She actually didn't get to see the film until years later, either. The 1994 film also included her first kiss, which was with none other than Brad Pitt, though neither were enthused! Dunst also wore the blue dress when she attended Rice's Memnoch Ball in 1995.
