@Bill ********
How long do you plan to stay on your next trip?
When do you plan to take her to the USA (i.e. are you anticipating more trips to Thailand after December before you are officially married)?
Are you over 50 and do you have any history in Thailand before April this year?
Did you enter and extend in April or did you enter, leave then come back again to get 45 days?
If you are not over 50 it looks like your cheap visa options will be either Single or Multiple entry tourist visas.
If over 50 then you could get a Non-Immigrant O visa based on retirement.
You shouldn't have an issue with the 66 days and pattern you have mentioned so far but in the end it's up to the IO.