I don't believe you will have an issue even IF a police background check was required. I don't believe anything before 18 would be checked AND if you are in a different state now, the check will only go back to when you started living in that state if you go to local/state police office to get the report. That is how it worked for me 7-8 years ago.
I use Charles Schwab bank to bank for LARGE international transfers. At the time when I researched this, Wise was better for under 20,000USD (637K THB), but over that amount, Schwab bank to bank transfers were more cost effective. I do two 1M+ baht wire transfers a year so use Schwab. Fee is $15 no matter amount transferred.
It's not that expensive here. You can get 3,5,10M baht comprehensive coverage here. With no claims in 4 years my 5M baht coverage is 2,000USD per year (mid-60's).
I agree on finding a local insurance broker, they will give you options (if any) for your mother and costs. Self-pay, at either a Government hospital (much less expensive) or an international hospital is the other primary option. Or, if she can travel, even returning home for a procedure could be an option.