What does my mother-in-law need for a 30-day visa exemption upon arrival in Bangkok?

To attain a 30-day visa exemption at Suvarnabhumi Airport, your mother-in-law will need to provide her U.S. passport, which must be valid for at least six months from the date of entry. She should also have a return ticket or proof of onward travel within 30 days, and potentially evidence of sufficient funds for her stay.