There's no place on a tax return to declare non assessable income. Meaning, it doesn't exist, thus TRD has never heard of it. Good chance also that, without this income being considered assessable, you owe no taxes if other income is below exemptions and deductions -- and thus have no need to file. And that the gift exceeds 20M THB is also a non player, since it's the "giftee," not the "gifter" who declares this 20M as income. So, if over 20M, wifey needs to file and declare. You're still invisible.