Deborah Gardner was an “effervescent, empathetic, benevolent, steadfast and wanderlust soul.”It was those qualities, inscribed recently on a memorial plaque marking the anniversary of her death, that prompted the 23-year-old from Steilacoom to join the Peace Corps in 1975.Tuesday marked 50 years since Gardner was stabbed to death by a fellow Peace Corps volunteer. Though decades have past since her killing, her ex-boyfriend and a Californian who…