Nikki Manders is the main villainess from Reaper episode 1.13, "Acid Queen."
She was played by Erica Cerra, who also appeared as Emma Correia on Sanctuary.
In life, Nikki was a very competitive model who was consumed with jealous rage; believing that other models were prettier than her. Her jealousy led to Nikki burning her own sister's face off with acid, which resulted in her condemnation to Hell.
After escaping from Hell, the evil Nikki went on a murderous rampage; killing women she believes to be more beautiful then her. Nikki possessed the ability to produce acid from her fingers, and among her victims was a famous model who beat her out for a magazine cover. Nikki was encountered by Sam, Ben, and Sock, with Sam carrying a "bubble toy vessel" (a vessel resembling a bottle filled with bubble solution) to capture Nikki. Nikki escaped him the first time, and subsequently, she set her villainous sights on Andi. Nikki is finally vanquished by Sam when he successfully captures the villainess in the vessel, doing so in front of Andi.