Chiwi

Here's my personal experience. I used to just use my US passport. Then I forgot about overstay once. Was quite the ordeal to sort out and was told I had to use my Thai passport from now on. I have tried to just check in at airport counters w my US passport, but when I do, they check for the stamps, and when they see none, they ask if I have a Thai passport. I've done it enough times that I just always give them both. The Thai Passport to exit, the US passport to show I can enter where I am going. When I renew my US passport at the embassy here, when they see no visa's or entry stamps, they ask if I have Thai citizenship. I've dealt with one too many headaches to realize it's just easier to enter/exit on the Thai passport and renew it well before it expires. Thai passport renewals are very easy these days.

I have US and Thai citizenship. I am required to enter/exit Thailand on my Thai passport. Don't know if its law or not but immigration started enforcing one of the coups ago, to prevent people on their watch list leaving on a foreign passport.

I traveled earlier this year to the USA. My Thai passport had less than 6 months on it. I called the airline, they told me they would not let me board with less than 6 months on the Thai passport. That I had a US passport did not matter to them.

The 6 month concept is to ensure you have adequate buffer on your passport doesn't expire while you are abroad and cannot return, this applies to the Thai passport. Showing the US passport is to prove that you can validly enter where you are going. The rules are not written with dual passports in mind. To ask check in to use logic to supersede the rules is a risk.

I have two passports, my child has two passports. Your daughter should leave/enter Thailand on her Thai passport. If you try to leave on a US passport with no entry stamps, immigration is going to have lots of questions. When you check in, you will need to show the US passport, if they see no entry stamp, they will ask for the Thai passport. I fly a lot, I always have to show check in both passports. If you have less than 6 months on the Thai passport, they probably will deny you boarding. You could try to argue w the check in that the US passport will get you into America, and that you don't need 6 months on the Thai passport to return, good luck with that. Or you can just get it renewed and not take the risk. Also, I suggest renewing US passport in Thailand via mail. US passports renewal processing time is up to 3 months now in the states. International renewals are less impacted by delays. I did mine a few months ago and it took 5 weeks.