I have a friend (US passport) who will be arriving to BKK next week. Her plan is to enter visa exempt for 30 days and then transit to Cambodia and Laos and eventually return to Thailand either visa exempt or on a 60 day SETV. She does not currently have proof of onward travel though she will be bringing 20,000b equivalent. Her planned stay in the region is 90 days total.
What is a good itinerary and plan to avoid any hassles with immigration?