correct. Unless you get a fiance visa to marry the gf once she is in the US, getting a tourist visa for a gf can be very hard, particularly if she is from Thailand. It is even harder if she doesn't have a good job, own a home and have significant ties to Thailand evidencing that she will return to Thailand.
foreign marriages are recognized. The issue is how long it takes to get the fiance/spouse into the US. In the US, you have to apply to bring your fiance (with the intent to get married) or wife (if already married) into the US. Both processes take several months assuming things go smoothly and there are no delays. There are also financial requirements that many people cannot satisfy.
it's never been next to impossible. It has just taken some time. And under trump, it takes even longer. Under trump, the worst part is the denial of work visas. For example, the Trump Administration has been denying visas for doctors arguing that doctors don't require bachelor's degrees.
There is no quick easy way. And if visas are processed in a similar manner to the last time trump was president, things are even harder than before. The non exclusive list of options are fiance visa, marriage visa, student visa, or there may be employment options for her depending on her qualifications and employer.
more taxes are coming. Make sure you get someone to help you plan if she has significant assets, particularly assets that may be subject to capital gains. (The US taxes on worldwide income.)