Need to arrange visa for 90 days max within 180 days period. Look at the Vfs website for all the papers you need to fill in (application, guarantee statement (to be legislated), passport copies, proof that she will return to Thailand, travel insurance and reservation for planeticket. Then make appointment for her at Vfs Bangkok, handin papers and passport. When approved they will send passport back to her with visa stamp. If not approved you can go into appeal but that will take additional 2 to 3 months
Pcr test is no longer required. I fly April 2nd and contacted my airlines. They confirmed that's no longer required from April onwards. However, always good to check with the airlines as they work with their systems and these need to be updated with that information. Can also be that you have a transfer flight and that that country even still requires negative Pcr evidence for transfers. Better be safe then sorry