Well, I that you do not want her to leave the U.S., file a divorce in Thailand, wait for that to process which I cannot even tell you about their laws and how long it could take, then file for her to get a visa to come back and that process I can tell you that it takes 9 months or so. So assuming that, she will most likely end up illegally in the U.S. at some point. She can try to extend her stay by filing an I-539 and proving why she needs to extend her stay, that she is not intending to immigrate and that she will go back home. If she mentions you, they will deny the extension. If they deny her extension and/or she overstays and stays illegally, marriage to a U.S. Citizen and filing the proper paperwork will put her back into legal status. So it really is not a big deal. The reason she needs more time is that to be able to file the divorce here, where she is now living, she will most likely have to be there for 6 months or more for the local family courts to have jurisdiction over her case. When that happens, she can file for the divorce and that could take 1 to 6 months or so. After the divorce is completed, then you will need to file an adjustment package. This includes the following forms: I-130 (Petition for family member), I-485 (application for Lawful Permanent Residency), I-765 (Application for work permit), I-131 (Application for Advance Parole), G-325a (Biographic data - one for each of you), I-693 (Medical exam that a certified doctor must fill), and I-864 (Affidavit of support). You will need to file each form with supporting evidence and appropriate filing fees. You can find these forms at www.uscis.gov/forms.
The supporting evidence that you would file would be birth certificates, marriage certificate, divorce certificates if either of you have been married previously, proof of your U.S. Citizenship, proof of your spouse's legal entry into the U.S., and financial documents to prove your income over the last year at least.
In about 3 to 5 months after filing, she should get a work permit and Advance Parole. About 5 to 7 months after filing you should get a marriage interview. If all goes well, a few weeks later she should get a Residency status (green card).
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