How fast did they return from scuba diving in Belize? The usual conservative recommendation is to wait 24 hours before going up high, which includes flying in a passenger jet. The Mauna Kea (13.8K) visitor center in Hawaii advises 24 hours.
So I wonder if she really was suffering from decompression sickness or was just dehydrated and exhausted.
You are quite right about the timeframe. Commercial airliners are kept at equivalent altitude of 7,000-8,000 ft so any decompression illness would have been then. Her symptoms on Whitney were unrelated to the diving.