Rachel

Rachel, also known as Paula, is one of the human assistants to Bianca St. Claire. She first appears in Storm Front.

Storm Front
In Storm Front, she was fed upon by Bianca St. Claire and killed. She did so willingly and with pleasure, a state that Harry Dresden reasons is caused by a component of a vampire's venom, maybe a narcotic of some sort.

Grave Peril
In Grave Peril, her death incites Bianca St. Claire to seek revenge against Harry Dresden, who she feels is responsible.

Her ghost visits Dresden while he's locked in a storage room in Bianca's mansion after being attacked by numerous vampires. She is tired and wants to be freed from Bianca.

Rachel's ghost, among a horde of other Bianca's victims that Dresden calls up, goes after Bianca, and brings her down.