GLAM GAL: "You only do prom once, and I've been planning this for over a year," says Brooklyn 17-year-old Jenna Cossuto. Photo: Graham Morrison Jenna Cossuto spent $2,400 on her custom-made dress. She'll rent a 22-seat stretch Hummer to transport her closest friends to privately booked Gotham Hall. And then it's off to the swanky South Street Seaport at Bridgewater and afterward, a party in Crobar's VIP section before a long weekend in a Hamptons beach house. But this once-in-a-lifetime weekend isn't for Cossuto's wedding. It's for this 17-year-old's senior prom. She's part of a growing generation of teens...
