Together Cheung and Dowling investigated a number of mysterious deaths in which the corpses were unmarked and had no sign of death. They came across Buffy Summers right after witnessing her stake a vampire and arrested her. Ironically, Dowling had came up with the theory that the bodies were those of vampires. Buffy escaped police custody, becoming a fugitive from the law, though she was ultimately cleared of all charges when they discovered that the real culprit was Severin, who possessed the ability to drain the energy of mystical beings.
Later, Cheung and Dowling were involved in a massive battle with a nest of "zompires", during which Cheung was overwhelmed and drained of blood, only to rise as a zompire herself. Dowling, along with Xander and Dawn, managed to track the newly risen Cheung to a bar where she had been on a feeding frenzy, where, after a hectic battle, they managed to stake her.
Behind the Scenes
Cheung's name is revealed in the script for Freefall #1, while her first name is revealed in Apart (of Me) #1, while Dowling is mourning her death.
Judging by her name and appearance, Cheung is of Chinese descent.