Qatar follows the requirements by the country you are entering. I did Antigen (rapid) test to come to the UK according to the UK requirements and on returning to Thailand I have to do RT-PCR according to the Thai government rules. I'm on Qatar also
7 days double vaxed, 10 days 1 vax and 14 days no vax is my guess. She could also apply to travel to Phuket first and stay 7 days and be allowed to travel around Phuket without quarantine as I understand.
I recommend booking with Randox on arrival who are at the airports. Took me 5 mins after exiting baggage area at Manchester and then it was done and didn't need to worry getting to a testing center in the next 2 days.
Tina Vander Wielen the reason I mentioned is because I saw a few people say Ethiad require their passengers to have a PCR. So if someone advises that thais don't need by government rules, you could then have got caught out by your airline rules. I have arranged for my son who carries a Thai passport a test even though I don't think Thais need the PCR prior to boarding, but I wasn't 100% sure, so I just booked him.