It is much simpler than you think, if you don't meet the financial requirements, all you need to do is find the cosponsor file an additional affidavit of support alongside yours. Begin by contacting the US accountant or CPA. There are some in South Korea which can be recommended by the US Embassy in Seoul. US citizens have to file tax returns even when living and working abroad. I hope you have, but not the tragedy if you have not, since a good accountant can file tax returns in arrears for the last four years or amend your current tax returns. Begin from there.
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You're confused. You, the immigrant, don't have to prove your income. It is the US citizen who does. If they don't make enough, you can find any US citizen or green card holder to be a joint sponsor. I hope this helps!
You can get a co-sponsor (friend/family?)
Since you'll be processing her papers in Korea (I hope that, in your, rush, she didn't enter the US yet) you will have time to document your income later.
IF she is in the US ... talk to a lawyer immediately!!!!!!!!
PROFESSOR OF IMMIGRATION LAW for over 10 years -- This blog posting is offered for informational purposes only. It does not constitute an attorney-client relationship. Also, keep in mind that this is an INTERNET BLOG. You should not rely on anything you read here to make decisions which impact on your life. Meet with an attorney, via Skype, or in person, to obtain competent personal and professional guidance.