You don’t have to apply while physically being in the US. They told me that lie too. I just asked for the form (so I can fill it out on the plane to LA, 555). I filled out the form, mailed it to my Mom in the US and told her to mail it in. They will only take applications mailed from within the US.
My Thai wife (from the countryside) was determined to get this done 35 years ago. She got it done in 4 months.
As another person stated “what you want to do is nearly impossible”.
But, what my wife did was get a fiancé visa to the US (K1) and we had to get married within 90 days. Been married ever since. Let me help you understand…I am smarter than the average person and if left completely up to me get this done, I would have never succeeded. You can message my wife (Kwan) if you think it will help. Good luck.
Sorry to report that if your girlfriend is not highly educated, is from Isan, has darker than white skin and is not a landowner and not a multimillionaire (Thai Baht), then it will be extremely difficult or worse. Easiest visa to get is a fiancé visa to your home country. That should only take 2 years or so. Good luck.