The pending I-130 will be converted to I-360. She can self petition. She has to go to the interview.
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My colleague is correct. I do suggest that your cousin get some help to make sure everything goes smoothly.
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Your cousin should retain counsel before attending her interview. The I-360 petition by widow/widower of a US citizen occurs where the I-130 was previously filed, and the USC spouse dies prior to adjustment of status of the beneficiary spouse. Make sure that she brings death certificate, birth certificate, or other documentation of decedent to the interview...
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I agree with the advice given by all of my colleagues but will add that if your cousin filed it without advice of an immigration attorney there could be issued that were never addressed.