We have reservations for four on Friday for a non-stop flight to Florida. My high school age daughter has decided not to go on the trip due to school exams. The flight only cost 98 bucks total and it's a 90.00 fee to change the ticket---so it's not worth it. We'd love to just take advantage of her empty seat (which right now is a booked middle seat between me and her sister) for more space since we've paid for it. How can we assure they just don't count her as a "no show" and fill the seat with a stand-by passenger?