You can apply for the retirement visa and if you don’t have the 800,000 baht to put in your account, there are visa agents that can put their money in an account in your name for a fee.
It’ll be very difficult and time-consuming to get her to the US before you’re married or after. It takes years. I know. The US consular officials that approve visas are now held accountable whenever someone, who they issued a visa to, overstays. As a result, most of them severely curtailed the number of visas they approved. They get paid the same whether or not they issue visas.