. So some people use this visa for staying almost 15 months. If you plan it a bit, and you come back just before the visa expires, you get another 90 days ! But for you not relevant I guess.
You also can ask for a Non imm. O MULTIPLE Entry in your home country. Then you need only one border bounce to get another 90 days. (Visa is valid for 1 year and every time when you leave and come back you get 90 days as long as your visa is valid)
If you have enough money in your Thai bank account (800k฿ 2 months before you ask the year extension) it's ofcourse possible to get a year extension. Maybe also ask a re-entry permit then, should you come back within that year.
I think it is wise to legalize your American marriage in Thailand too when you are here. This for future use ? ('Only' 400k฿ in your bank account needed or 12x 40k฿ per month as international transfer instead of 65k฿ per month
There IS a form which normaly will be accepted by many imm. offices for a home country insurance. But...I hear/read that that form is difficult to get it signed by your home insurance company. Maybe give it a try ? (See form at my own answer)
, I know this one. They asked this 2 times at Korat imm., signed by my (Thai) girlfriend. The last 3 times when I went for my year extension, they gave it back to me. So not sure who has to fill it in for your friend. Maybe they gave it to your friend 'standard' because many of us have a Thai partner.🤷♂️