Erin's superior officer was lawman Broder. On opposing sides already because of her job as a cop and Melaka's thieving, Erin also blamed Mel for the death of their brother for a long time.
The two sisters eventually reconciled when Mel sought her to tell her that she was the Slayer and their brother was a vampire. Erin initially refused to believe her, but she got to crash her flying car on top of the lurk Icarus while he challenged Mel, as revenge for murdering her brother. The sisters then joined forces in the big battle against Harth's army of lurks and the Old OneNeauth.