The valedictorian of yesterday’s graduating police academy class, Karolina Wierzchowska, is no stranger to challenges. Fresh out of high school, Ms. Wierzchowska left her mother and younger brother in Poland and moved to New York City to pursue her dreams. “My father invited me to live with him in America,” the 5-foot-1-inch Ms. Wierzchowska told her 913 fellow academy graduates at a …