Graham W Stanley. She may need to reschedule the Cambodia flight, as I think it's unlikely she would have the time to travel to quarantine hotel (although there are some in the close vicinity of the airport), undertake the test and then wait for test results. It seems a very tight timeline.
She will need to enter Thailand, so she's not a transit passenger. She will have to apply for a Thailand Pass. Assuming she's fully vaxxed, she can do Test & Go, but will need one night in a SHA+ hotel.
Covid extension now only allowed for TR and exempt stamps. All non-immigrant visas now required standard extension, or if not available leave/re-enter country
Mark Nissel. It's completely different to how it was before. Non-immigrant visas can no longer get covid extension. We've already had one guy directed to leave within seven days. Whatever you wish to believe is fine, but it's been months since anyone has been "unable to return to their home country". Flights are in abundance now.