So many sad things in this story, not the least of which is a 14 year old too fat to fit in an airplane seat.

I do note that the word "standby" was slipped in, almost un-noticed. WN required pax requiring 2 seats to pay for 2 seats if the flight it full, but not otherwide. Here, the flight was not full with existing reservations, but then was filled with a standby passenger. I suppose that's the right call - the passenger in question flew on the flight ticketed.