(Covers information from the D.C. comics)
Lesley was the fiancée of Stan. She worked at a hospital (whether as a doctor or nurse is unknown). She and Stan took a fateful vacation to Isla Bonale, and were the only two people to avoid the deadly effects of the G-Virus because they were out snorkelling when the Umbrella plane carrying it crashed on the island.
Although she survived an attack by the zombified Ace, a giant, mutant eel, man-eating plants and giant lizards, not to mention the crashed plane's additional cargo of Lickers, in order to reach the resort's radio station, it was all in vain. Both she and Stan were shot and killed by William Birkin when an Umbrella containment squad arrived.