As seven skydivers jumped out of a plane Thursday afternoon and began to fall back toward the ground in Northern California, a gust of air seized control of a 28-year-old woman’s parachute. She struggled, witnesses said, as the wind carried her away from the Skydive Lodi Parachute Center’s safe landing zone, careening toward the flow of traffic on California Highway 99 in Acampo, Calif., about 90 miles northeast of San Francisco.